2020-02-17 16:12:04 +00:00
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.. SPDX-License-Identifier: GPL-2.0
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==========================================
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2012-11-02 08:05:42 +00:00
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WHAT IS Flash-Friendly File System (F2FS)?
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2020-02-17 16:12:04 +00:00
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==========================================
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2012-11-02 08:05:42 +00:00
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NAND flash memory-based storage devices, such as SSD, eMMC, and SD cards, have
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been equipped on a variety systems ranging from mobile to server systems. Since
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they are known to have different characteristics from the conventional rotating
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disks, a file system, an upper layer to the storage device, should adapt to the
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changes from the sketch in the design level.
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F2FS is a file system exploiting NAND flash memory-based storage devices, which
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is based on Log-structured File System (LFS). The design has been focused on
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addressing the fundamental issues in LFS, which are snowball effect of wandering
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tree and high cleaning overhead.
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Since a NAND flash memory-based storage device shows different characteristic
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according to its internal geometry or flash memory management scheme, namely FTL,
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F2FS and its tools support various parameters not only for configuring on-disk
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layout, but also for selecting allocation and cleaning algorithms.
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2013-07-04 08:12:47 +00:00
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The following git tree provides the file system formatting tool (mkfs.f2fs),
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a consistency checking tool (fsck.f2fs), and a debugging tool (dump.f2fs).
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2020-02-17 16:12:04 +00:00
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- git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs-tools.git
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2012-11-27 05:36:14 +00:00
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2022-11-26 02:38:07 +00:00
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For sending patches, please use the following mailing list:
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2012-11-02 08:05:42 +00:00
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2020-02-17 16:12:04 +00:00
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- linux-f2fs-devel@lists.sourceforge.net
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2022-11-26 02:38:07 +00:00
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For reporting bugs, please use the following f2fs bug tracker link:
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- https://bugzilla.kernel.org/enter_bug.cgi?product=File%20System&component=f2fs
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2020-02-17 16:12:04 +00:00
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Background and Design issues
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============================
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2012-11-02 08:05:42 +00:00
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Log-structured File System (LFS)
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--------------------------------
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"A log-structured file system writes all modifications to disk sequentially in
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a log-like structure, thereby speeding up both file writing and crash recovery.
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The log is the only structure on disk; it contains indexing information so that
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files can be read back from the log efficiently. In order to maintain large free
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areas on disk for fast writing, we divide the log into segments and use a
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segment cleaner to compress the live information from heavily fragmented
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segments." from Rosenblum, M. and Ousterhout, J. K., 1992, "The design and
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implementation of a log-structured file system", ACM Trans. Computer Systems
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10, 1, 26–52.
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Wandering Tree Problem
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----------------------
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In LFS, when a file data is updated and written to the end of log, its direct
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pointer block is updated due to the changed location. Then the indirect pointer
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block is also updated due to the direct pointer block update. In this manner,
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the upper index structures such as inode, inode map, and checkpoint block are
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also updated recursively. This problem is called as wandering tree problem [1],
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and in order to enhance the performance, it should eliminate or relax the update
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propagation as much as possible.
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[1] Bityutskiy, A. 2005. JFFS3 design issues. http://www.linux-mtd.infradead.org/
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Cleaning Overhead
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-----------------
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Since LFS is based on out-of-place writes, it produces so many obsolete blocks
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scattered across the whole storage. In order to serve new empty log space, it
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needs to reclaim these obsolete blocks seamlessly to users. This job is called
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as a cleaning process.
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The process consists of three operations as follows.
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2012-11-02 08:05:42 +00:00
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1. A victim segment is selected through referencing segment usage table.
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2. It loads parent index structures of all the data in the victim identified by
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segment summary blocks.
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3. It checks the cross-reference between the data and its parent index structure.
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4. It moves valid data selectively.
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This cleaning job may cause unexpected long delays, so the most important goal
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is to hide the latencies to users. And also definitely, it should reduce the
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amount of valid data to be moved, and move them quickly as well.
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2020-02-17 16:12:04 +00:00
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Key Features
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============
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2012-11-02 08:05:42 +00:00
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Flash Awareness
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---------------
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- Enlarge the random write area for better performance, but provide the high
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spatial locality
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- Align FS data structures to the operational units in FTL as best efforts
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Wandering Tree Problem
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----------------------
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- Use a term, “node”, that represents inodes as well as various pointer blocks
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- Introduce Node Address Table (NAT) containing the locations of all the “node”
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blocks; this will cut off the update propagation.
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Cleaning Overhead
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-----------------
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- Support a background cleaning process
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- Support greedy and cost-benefit algorithms for victim selection policies
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- Support multi-head logs for static/dynamic hot and cold data separation
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- Introduce adaptive logging for efficient block allocation
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2020-02-17 16:12:04 +00:00
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Mount Options
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=============
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2012-11-02 08:05:42 +00:00
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2020-02-17 16:12:04 +00:00
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2020-06-22 13:35:39 +00:00
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======================== ============================================================
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background_gc=%s Turn on/off cleaning operations, namely garbage
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collection, triggered in background when I/O subsystem is
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idle. If background_gc=on, it will turn on the garbage
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collection and if background_gc=off, garbage collection
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will be turned off. If background_gc=sync, it will turn
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on synchronous garbage collection running in background.
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Default value for this option is on. So garbage
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collection is on by default.
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2021-03-27 09:57:06 +00:00
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gc_merge When background_gc is on, this option can be enabled to
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let background GC thread to handle foreground GC requests,
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it can eliminate the sluggish issue caused by slow foreground
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GC operation when GC is triggered from a process with limited
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I/O and CPU resources.
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nogc_merge Disable GC merge feature.
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2020-06-22 13:35:39 +00:00
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disable_roll_forward Disable the roll-forward recovery routine
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norecovery Disable the roll-forward recovery routine, mounted read-
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only (i.e., -o ro,disable_roll_forward)
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discard/nodiscard Enable/disable real-time discard in f2fs, if discard is
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enabled, f2fs will issue discard/TRIM commands when a
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segment is cleaned.
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2024-02-20 20:48:44 +00:00
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heap/no_heap Deprecated.
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nouser_xattr Disable Extended User Attributes. Note: xattr is enabled
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by default if CONFIG_F2FS_FS_XATTR is selected.
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noacl Disable POSIX Access Control List. Note: acl is enabled
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by default if CONFIG_F2FS_FS_POSIX_ACL is selected.
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active_logs=%u Support configuring the number of active logs. In the
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current design, f2fs supports only 2, 4, and 6 logs.
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Default number is 6.
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disable_ext_identify Disable the extension list configured by mkfs, so f2fs
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2020-09-03 00:08:31 +00:00
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is not aware of cold files such as media files.
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inline_xattr Enable the inline xattrs feature.
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noinline_xattr Disable the inline xattrs feature.
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inline_xattr_size=%u Support configuring inline xattr size, it depends on
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flexible inline xattr feature.
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2020-09-03 00:08:31 +00:00
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inline_data Enable the inline data feature: Newly created small (<~3.4k)
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files can be written into inode block.
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2020-09-03 00:08:31 +00:00
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inline_dentry Enable the inline dir feature: data in newly created
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directory entries can be written into inode block. The
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space of inode block which is used to store inline
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dentries is limited to ~3.4k.
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noinline_dentry Disable the inline dentry feature.
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flush_merge Merge concurrent cache_flush commands as much as possible
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to eliminate redundant command issues. If the underlying
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device handles the cache_flush command relatively slowly,
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recommend to enable this option.
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nobarrier This option can be used if underlying storage guarantees
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its cached data should be written to the novolatile area.
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If this option is set, no cache_flush commands are issued
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but f2fs still guarantees the write ordering of all the
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data writes.
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2022-12-13 15:08:37 +00:00
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barrier If this option is set, cache_flush commands are allowed to be
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2022-10-24 17:54:01 +00:00
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issued.
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2020-06-22 13:35:39 +00:00
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fastboot This option is used when a system wants to reduce mount
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time as much as possible, even though normal performance
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can be sacrificed.
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extent_cache Enable an extent cache based on rb-tree, it can cache
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as many as extent which map between contiguous logical
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address and physical address per inode, resulting in
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increasing the cache hit ratio. Set by default.
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noextent_cache Disable an extent cache based on rb-tree explicitly, see
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the above extent_cache mount option.
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noinline_data Disable the inline data feature, inline data feature is
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enabled by default.
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data_flush Enable data flushing before checkpoint in order to
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persist data of regular and symlink.
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reserve_root=%d Support configuring reserved space which is used for
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allocation from a privileged user with specified uid or
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gid, unit: 4KB, the default limit is 0.2% of user blocks.
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resuid=%d The user ID which may use the reserved blocks.
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resgid=%d The group ID which may use the reserved blocks.
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fault_injection=%d Enable fault injection in all supported types with
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specified injection rate.
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fault_type=%d Support configuring fault injection type, should be
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enabled with fault_injection option, fault type value
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is shown below, it supports single or combined type.
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2020-02-17 16:12:04 +00:00
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2024-01-12 19:41:32 +00:00
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=========================== ===========
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Type_Name Type_Value
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=========================== ===========
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FAULT_KMALLOC 0x000000001
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FAULT_KVMALLOC 0x000000002
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FAULT_PAGE_ALLOC 0x000000004
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FAULT_PAGE_GET 0x000000008
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FAULT_ALLOC_BIO 0x000000010 (obsolete)
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FAULT_ALLOC_NID 0x000000020
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FAULT_ORPHAN 0x000000040
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FAULT_BLOCK 0x000000080
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FAULT_DIR_DEPTH 0x000000100
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FAULT_EVICT_INODE 0x000000200
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FAULT_TRUNCATE 0x000000400
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FAULT_READ_IO 0x000000800
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FAULT_CHECKPOINT 0x000001000
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FAULT_DISCARD 0x000002000
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FAULT_WRITE_IO 0x000004000
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FAULT_SLAB_ALLOC 0x000008000
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FAULT_DQUOT_INIT 0x000010000
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FAULT_LOCK_OP 0x000020000
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FAULT_BLKADDR_VALIDITY 0x000040000
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FAULT_BLKADDR_CONSISTENCE 0x000080000
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2024-02-22 12:18:51 +00:00
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FAULT_NO_SEGMENT 0x000100000
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2024-01-12 19:41:32 +00:00
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=========================== ===========
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2020-06-22 13:35:39 +00:00
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mode=%s Control block allocation mode which supports "adaptive"
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and "lfs". In "lfs" mode, there should be no random
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writes towards main area.
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2021-09-29 18:12:03 +00:00
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"fragment:segment" and "fragment:block" are newly added here.
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These are developer options for experiments to simulate filesystem
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fragmentation/after-GC situation itself. The developers use these
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modes to understand filesystem fragmentation/after-GC condition well,
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and eventually get some insights to handle them better.
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In "fragment:segment", f2fs allocates a new segment in ramdom
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position. With this, we can simulate the after-GC condition.
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In "fragment:block", we can scatter block allocation with
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"max_fragment_chunk" and "max_fragment_hole" sysfs nodes.
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We added some randomness to both chunk and hole size to make
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it close to realistic IO pattern. So, in this mode, f2fs will allocate
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1..<max_fragment_chunk> blocks in a chunk and make a hole in the
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length of 1..<max_fragment_hole> by turns. With this, the newly
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allocated blocks will be scattered throughout the whole partition.
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Note that "fragment:block" implicitly enables "fragment:segment"
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option for more randomness.
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Please, use these options for your experiments and we strongly
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recommend to re-format the filesystem after using these options.
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2020-06-22 13:35:39 +00:00
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usrquota Enable plain user disk quota accounting.
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grpquota Enable plain group disk quota accounting.
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prjquota Enable plain project quota accounting.
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usrjquota=<file> Appoint specified file and type during mount, so that quota
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grpjquota=<file> information can be properly updated during recovery flow,
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prjjquota=<file> <quota file>: must be in root directory;
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jqfmt=<quota type> <quota type>: [vfsold,vfsv0,vfsv1].
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2020-09-03 00:08:31 +00:00
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offusrjquota Turn off user journalled quota.
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offgrpjquota Turn off group journalled quota.
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offprjjquota Turn off project journalled quota.
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2020-06-22 13:35:39 +00:00
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quota Enable plain user disk quota accounting.
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noquota Disable all plain disk quota option.
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alloc_mode=%s Adjust block allocation policy, which supports "reuse"
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and "default".
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fsync_mode=%s Control the policy of fsync. Currently supports "posix",
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"strict", and "nobarrier". In "posix" mode, which is
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default, fsync will follow POSIX semantics and does a
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light operation to improve the filesystem performance.
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In "strict" mode, fsync will be heavy and behaves in line
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with xfs, ext4 and btrfs, where xfstest generic/342 will
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|
|
|
|
pass, but the performance will regress. "nobarrier" is
|
|
|
|
|
|
based on "posix", but doesn't issue flush command for
|
|
|
|
|
|
non-atomic files likewise "nobarrier" mount option.
|
fscrypt: support test_dummy_encryption=v2
v1 encryption policies are deprecated in favor of v2, and some new
features (e.g. encryption+casefolding) are only being added for v2.
Therefore, the "test_dummy_encryption" mount option (which is used for
encryption I/O testing with xfstests) needs to support v2 policies.
To do this, extend its syntax to be "test_dummy_encryption=v1" or
"test_dummy_encryption=v2". The existing "test_dummy_encryption" (no
argument) also continues to be accepted, to specify the default setting
-- currently v1, but the next patch changes it to v2.
To cleanly support both v1 and v2 while also making it easy to support
specifying other encryption settings in the future (say, accepting
"$contents_mode:$filenames_mode:v2"), make ext4 and f2fs maintain a
pointer to the dummy fscrypt_context rather than using mount flags.
To avoid concurrency issues, don't allow test_dummy_encryption to be set
or changed during a remount. (The former restriction is new, but
xfstests doesn't run into it, so no one should notice.)
Tested with 'gce-xfstests -c {ext4,f2fs}/encrypt -g auto'. On ext4,
there are two regressions, both of which are test bugs: ext4/023 and
ext4/028 fail because they set an xattr and expect it to be stored
inline, but the increase in size of the fscrypt_context from
24 to 40 bytes causes this xattr to be spilled into an external block.
Link: https://lore.kernel.org/r/20200512233251.118314-4-ebiggers@kernel.org
Acked-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
2020-05-12 23:32:50 +00:00
|
|
|
|
test_dummy_encryption
|
|
|
|
|
|
test_dummy_encryption=%s
|
2020-06-22 13:35:39 +00:00
|
|
|
|
Enable dummy encryption, which provides a fake fscrypt
|
|
|
|
|
|
context. The fake fscrypt context is used by xfstests.
|
|
|
|
|
|
The argument may be either "v1" or "v2", in order to
|
|
|
|
|
|
select the corresponding fscrypt policy version.
|
|
|
|
|
|
checkpoint=%s[:%u[%]] Set to "disable" to turn off checkpointing. Set to "enable"
|
|
|
|
|
|
to reenable checkpointing. Is enabled by default. While
|
|
|
|
|
|
disabled, any unmounting or unexpected shutdowns will cause
|
|
|
|
|
|
the filesystem contents to appear as they did when the
|
|
|
|
|
|
filesystem was mounted with that option.
|
2023-04-09 05:29:51 +00:00
|
|
|
|
While mounting with checkpoint=disable, the filesystem must
|
2020-06-22 13:35:39 +00:00
|
|
|
|
run garbage collection to ensure that all available space can
|
|
|
|
|
|
be used. If this takes too much time, the mount may return
|
|
|
|
|
|
EAGAIN. You may optionally add a value to indicate how much
|
|
|
|
|
|
of the disk you would be willing to temporarily give up to
|
|
|
|
|
|
avoid additional garbage collection. This can be given as a
|
|
|
|
|
|
number of blocks, or as a percent. For instance, mounting
|
|
|
|
|
|
with checkpoint=disable:100% would always succeed, but it may
|
|
|
|
|
|
hide up to all remaining free space. The actual space that
|
|
|
|
|
|
would be unusable can be viewed at /sys/fs/f2fs/<disk>/unusable
|
|
|
|
|
|
This space is reclaimed once checkpoint=enable.
|
f2fs: introduce checkpoint_merge mount option
We've added a new mount options, "checkpoint_merge" and "nocheckpoint_merge",
which creates a kernel daemon and makes it to merge concurrent checkpoint
requests as much as possible to eliminate redundant checkpoint issues. Plus,
we can eliminate the sluggish issue caused by slow checkpoint operation
when the checkpoint is done in a process context in a cgroup having
low i/o budget and cpu shares. To make this do better, we set the
default i/o priority of the kernel daemon to "3", to give one higher
priority than other kernel threads. The below verification result
explains this.
The basic idea has come from https://opensource.samsung.com.
[Verification]
Android Pixel Device(ARM64, 7GB RAM, 256GB UFS)
Create two I/O cgroups (fg w/ weight 100, bg w/ wight 20)
Set "strict_guarantees" to "1" in BFQ tunables
In "fg" cgroup,
- thread A => trigger 1000 checkpoint operations
"for i in `seq 1 1000`; do touch test_dir1/file; fsync test_dir1;
done"
- thread B => gererating async. I/O
"fio --rw=write --numjobs=1 --bs=128k --runtime=3600 --time_based=1
--filename=test_img --name=test"
In "bg" cgroup,
- thread C => trigger repeated checkpoint operations
"echo $$ > /dev/blkio/bg/tasks; while true; do touch test_dir2/file;
fsync test_dir2; done"
We've measured thread A's execution time.
[ w/o patch ]
Elapsed Time: Avg. 68 seconds
[ w/ patch ]
Elapsed Time: Avg. 48 seconds
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
[Jaegeuk Kim: fix the return value in f2fs_start_ckpt_thread, reported by Dan]
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Sungjong Seo <sj1557.seo@samsung.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2021-01-19 00:00:42 +00:00
|
|
|
|
checkpoint_merge When checkpoint is enabled, this can be used to create a kernel
|
|
|
|
|
|
daemon and make it to merge concurrent checkpoint requests as
|
|
|
|
|
|
much as possible to eliminate redundant checkpoint issues. Plus,
|
|
|
|
|
|
we can eliminate the sluggish issue caused by slow checkpoint
|
|
|
|
|
|
operation when the checkpoint is done in a process context in
|
|
|
|
|
|
a cgroup having low i/o budget and cpu shares. To make this
|
|
|
|
|
|
do better, we set the default i/o priority of the kernel daemon
|
|
|
|
|
|
to "3", to give one higher priority than other kernel threads.
|
|
|
|
|
|
This is the same way to give a I/O priority to the jbd2
|
|
|
|
|
|
journaling thread of ext4 filesystem.
|
|
|
|
|
|
nocheckpoint_merge Disable checkpoint merge feature.
|
2020-06-22 13:35:39 +00:00
|
|
|
|
compress_algorithm=%s Control compress algorithm, currently f2fs supports "lzo",
|
|
|
|
|
|
"lz4", "zstd" and "lzo-rle" algorithm.
|
2021-01-22 09:46:43 +00:00
|
|
|
|
compress_algorithm=%s:%d Control compress algorithm and its compress level, now, only
|
|
|
|
|
|
"lz4" and "zstd" support compress level config.
|
|
|
|
|
|
algorithm level range
|
|
|
|
|
|
lz4 3 - 16
|
|
|
|
|
|
zstd 1 - 22
|
2022-09-01 00:28:28 +00:00
|
|
|
|
compress_log_size=%u Support configuring compress cluster size. The size will
|
|
|
|
|
|
be 4KB * (1 << %u). The default and minimum sizes are 16KB.
|
2020-06-22 13:35:39 +00:00
|
|
|
|
compress_extension=%s Support adding specified extension, so that f2fs can enable
|
|
|
|
|
|
compression on those corresponding files, e.g. if all files
|
|
|
|
|
|
with '.ext' has high compression rate, we can set the '.ext'
|
|
|
|
|
|
on compression extension list and enable compression on
|
|
|
|
|
|
these file by default rather than to enable it via ioctl.
|
|
|
|
|
|
For other files, we can still enable compression via ioctl.
|
f2fs-for-5.9-rc1
In this round, we've added two small interfaces, 1) GC_URGENT_LOW mode for
performance, and 2) F2FS_IOC_SEC_TRIM_FILE ioctl for security. The new GC
mode allows Android to run some lower priority GCs in background, while new
ioctl discards user information without race condition when the account is
removed. In addition, some patches were merged to address latency-related
issues. We've fixed some compression-related bug fixes as well as edge race
conditions.
Enhancement:
- add GC_URGENT_LOW mode in gc_urgent
- introduce F2FS_IOC_SEC_TRIM_FILE ioctl
- bypass racy readahead to improve read latencies
- shrink node_write lock coverage to avoid long latency
Bug fix:
- fix missing compression flag control, i_size, and mount option
- fix deadlock between quota writes and checkpoint
- remove inode eviction path in synchronous path to avoid deadlock
- fix to wait GCed compressed page writeback
- fix a kernel panic in f2fs_is_compressed_page
- check page dirty status before writeback
- wait page writeback before update in node page write flow
- fix a race condition between f2fs_write_end_io and f2fs_del_fsync_node_entry
We've added some minor sanity checks and refactored trivial code blocks for
better readability and debugging information.
-----BEGIN PGP SIGNATURE-----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=PjaF
-----END PGP SIGNATURE-----
Merge tag 'f2fs-for-5.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs
Pull f2fs updates from Jaegeuk Kim:
"In this round, we've added two small interfaces: (a) GC_URGENT_LOW
mode for performance and (b) F2FS_IOC_SEC_TRIM_FILE ioctl for
security.
The new GC mode allows Android to run some lower priority GCs in
background, while new ioctl discards user information without race
condition when the account is removed.
In addition, some patches were merged to address latency-related
issues. We've fixed some compression-related bug fixes as well as edge
race conditions.
Enhancements:
- add GC_URGENT_LOW mode in gc_urgent
- introduce F2FS_IOC_SEC_TRIM_FILE ioctl
- bypass racy readahead to improve read latencies
- shrink node_write lock coverage to avoid long latency
Bug fixes:
- fix missing compression flag control, i_size, and mount option
- fix deadlock between quota writes and checkpoint
- remove inode eviction path in synchronous path to avoid deadlock
- fix to wait GCed compressed page writeback
- fix a kernel panic in f2fs_is_compressed_page
- check page dirty status before writeback
- wait page writeback before update in node page write flow
- fix a race condition between f2fs_write_end_io and f2fs_del_fsync_node_entry
We've added some minor sanity checks and refactored trivial code
blocks for better readability and debugging information"
* tag 'f2fs-for-5.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs: (52 commits)
f2fs: prepare a waiter before entering io_schedule
f2fs: update_sit_entry: Make the judgment condition of f2fs_bug_on more intuitive
f2fs: replace test_and_set/clear_bit() with set/clear_bit()
f2fs: make file immutable even if releasing zero compression block
f2fs: compress: disable compression mount option if compression is off
f2fs: compress: add sanity check during compressed cluster read
f2fs: use macro instead of f2fs verity version
f2fs: fix deadlock between quota writes and checkpoint
f2fs: correct comment of f2fs_exist_written_data
f2fs: compress: delay temp page allocation
f2fs: compress: fix to update isize when overwriting compressed file
f2fs: space related cleanup
f2fs: fix use-after-free issue
f2fs: Change the type of f2fs_flush_inline_data() to void
f2fs: add F2FS_IOC_SEC_TRIM_FILE ioctl
f2fs: should avoid inode eviction in synchronous path
f2fs: segment.h: delete a duplicated word
f2fs: compress: fix to avoid memory leak on cc->cpages
f2fs: use generic names for generic ioctls
f2fs: don't keep meta inode pages used for compressed block migration
...
2020-08-11 01:33:22 +00:00
|
|
|
|
Note that, there is one reserved special extension '*', it
|
|
|
|
|
|
can be set to enable compression for all files.
|
2021-10-23 02:58:33 +00:00
|
|
|
|
nocompress_extension=%s Support adding specified extension, so that f2fs can disable
|
2021-06-08 11:15:08 +00:00
|
|
|
|
compression on those corresponding files, just contrary to compression extension.
|
|
|
|
|
|
If you know exactly which files cannot be compressed, you can use this.
|
|
|
|
|
|
The same extension name can't appear in both compress and nocompress
|
|
|
|
|
|
extension at the same time.
|
|
|
|
|
|
If the compress extension specifies all files, the types specified by the
|
|
|
|
|
|
nocompress extension will be treated as special cases and will not be compressed.
|
|
|
|
|
|
Don't allow use '*' to specifie all file in nocompress extension.
|
|
|
|
|
|
After add nocompress_extension, the priority should be:
|
|
|
|
|
|
dir_flag < comp_extention,nocompress_extension < comp_file_flag,no_comp_file_flag.
|
|
|
|
|
|
See more in compression sections.
|
|
|
|
|
|
|
2020-11-26 10:32:09 +00:00
|
|
|
|
compress_chksum Support verifying chksum of raw data in compressed cluster.
|
2020-12-01 04:08:02 +00:00
|
|
|
|
compress_mode=%s Control file compression mode. This supports "fs" and "user"
|
|
|
|
|
|
modes. In "fs" mode (default), f2fs does automatic compression
|
|
|
|
|
|
on the compression enabled files. In "user" mode, f2fs disables
|
|
|
|
|
|
the automaic compression and gives the user discretion of
|
|
|
|
|
|
choosing the target file and the timing. The user can do manual
|
|
|
|
|
|
compression/decompression on the compression enabled files using
|
|
|
|
|
|
ioctls.
|
2021-05-20 11:51:50 +00:00
|
|
|
|
compress_cache Support to use address space of a filesystem managed inode to
|
|
|
|
|
|
cache compressed block, in order to improve cache hit ratio of
|
|
|
|
|
|
random read.
|
2020-08-05 05:47:54 +00:00
|
|
|
|
inlinecrypt When possible, encrypt/decrypt the contents of encrypted
|
|
|
|
|
|
files using the blk-crypto framework rather than
|
|
|
|
|
|
filesystem-layer encryption. This allows the use of
|
|
|
|
|
|
inline encryption hardware. The on-disk format is
|
|
|
|
|
|
unaffected. For more details, see
|
|
|
|
|
|
Documentation/block/inline-encryption.rst.
|
f2fs: support age threshold based garbage collection
There are several issues in current background GC algorithm:
- valid blocks is one of key factors during cost overhead calculation,
so if segment has less valid block, however even its age is young or
it locates hot segment, CB algorithm will still choose the segment as
victim, it's not appropriate.
- GCed data/node will go to existing logs, no matter in-there datas'
update frequency is the same or not, it may mix hot and cold data
again.
- GC alloctor mainly use LFS type segment, it will cost free segment
more quickly.
This patch introduces a new algorithm named age threshold based
garbage collection to solve above issues, there are three steps
mainly:
1. select a source victim:
- set an age threshold, and select candidates beased threshold:
e.g.
0 means youngest, 100 means oldest, if we set age threshold to 80
then select dirty segments which has age in range of [80, 100] as
candiddates;
- set candidate_ratio threshold, and select candidates based the
ratio, so that we can shrink candidates to those oldest segments;
- select target segment with fewest valid blocks in order to
migrate blocks with minimum cost;
2. select a target victim:
- select candidates beased age threshold;
- set candidate_radius threshold, search candidates whose age is
around source victims, searching radius should less than the
radius threshold.
- select target segment with most valid blocks in order to avoid
migrating current target segment.
3. merge valid blocks from source victim into target victim with
SSR alloctor.
Test steps:
- create 160 dirty segments:
* half of them have 128 valid blocks per segment
* left of them have 384 valid blocks per segment
- run background GC
Benefit: GC count and block movement count both decrease obviously:
- Before:
- Valid: 86
- Dirty: 1
- Prefree: 11
- Free: 6001 (6001)
GC calls: 162 (BG: 220)
- data segments : 160 (160)
- node segments : 2 (2)
Try to move 41454 blocks (BG: 41454)
- data blocks : 40960 (40960)
- node blocks : 494 (494)
IPU: 0 blocks
SSR: 0 blocks in 0 segments
LFS: 41364 blocks in 81 segments
- After:
- Valid: 87
- Dirty: 0
- Prefree: 4
- Free: 6008 (6008)
GC calls: 75 (BG: 76)
- data segments : 74 (74)
- node segments : 1 (1)
Try to move 12813 blocks (BG: 12813)
- data blocks : 12544 (12544)
- node blocks : 269 (269)
IPU: 0 blocks
SSR: 12032 blocks in 77 segments
LFS: 855 blocks in 2 segments
Signed-off-by: Chao Yu <yuchao0@huawei.com>
[Jaegeuk Kim: fix a bug along with pinfile in-mem segment & clean up]
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2020-08-04 13:14:49 +00:00
|
|
|
|
atgc Enable age-threshold garbage collection, it provides high
|
|
|
|
|
|
effectiveness and efficiency on background GC.
|
f2fs: introduce discard_unit mount option
As James Z reported in bugzilla:
https://bugzilla.kernel.org/show_bug.cgi?id=213877
[1.] One-line summary of the problem:
Mount multiple SMR block devices exceed certain number cause system non-response
[2.] Full description of the problem/report:
Created some F2FS on SMR devices (mkfs.f2fs -m), then mounted in sequence. Each device is the same Model: HGST HSH721414AL (Size 14TB).
Empirically, found that when the amount of SMR device * 1.5Gb > System RAM, the system ran out of memory and hung. No dmesg output. For example, 24 SMR Disk need 24*1.5GB = 36GB. A system with 32G RAM can only mount 21 devices, the 22nd device will be a reproducible cause of system hang.
The number of SMR devices with other FS mounted on this system does not interfere with the result above.
[3.] Keywords (i.e., modules, networking, kernel):
F2FS, SMR, Memory
[4.] Kernel information
[4.1.] Kernel version (uname -a):
Linux 5.13.4-200.fc34.x86_64 #1 SMP Tue Jul 20 20:27:29 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
[4.2.] Kernel .config file:
Default Fedora 34 with f2fs-tools-1.14.0-2.fc34.x86_64
[5.] Most recent kernel version which did not have the bug:
None
[6.] Output of Oops.. message (if applicable) with symbolic information
resolved (see Documentation/admin-guide/oops-tracing.rst)
None
[7.] A small shell script or example program which triggers the
problem (if possible)
mount /dev/sdX /mnt/0X
[8.] Memory consumption
With 24 * 14T SMR Block device with F2FS
free -g
total used free shared buff/cache available
Mem: 46 36 0 0 10 10
Swap: 0 0 0
With 3 * 14T SMR Block device with F2FS
free -g
total used free shared buff/cache available
Mem: 7 5 0 0 1 1
Swap: 7 0 7
The root cause is, there are three bitmaps:
- cur_valid_map
- ckpt_valid_map
- discard_map
and each of them will cost ~500MB memory, {cur, ckpt}_valid_map are
necessary, but discard_map is optional, since this bitmap will only be
useful in mountpoint that small discard is enabled.
For a blkzoned device such as SMR or ZNS devices, f2fs will only issue
discard for a section(zone) when all blocks of that section are invalid,
so, for such device, we don't need small discard functionality at all.
This patch introduces a new mountoption "discard_unit=block|segment|
section" to support issuing discard with different basic unit which is
aligned to block, segment or section, so that user can specify
"discard_unit=segment" or "discard_unit=section" to disable small
discard functionality.
Note that this mount option can not be changed by remount() due to
related metadata need to be initialized during mount().
In order to save memory, let's use "discard_unit=section" for blkzoned
device by default.
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2021-08-03 00:15:43 +00:00
|
|
|
|
discard_unit=%s Control discard unit, the argument can be "block", "segment"
|
|
|
|
|
|
and "section", issued discard command's offset/size will be
|
|
|
|
|
|
aligned to the unit, by default, "discard_unit=block" is set,
|
|
|
|
|
|
so that small discard functionality is enabled.
|
|
|
|
|
|
For blkzoned device, "discard_unit=section" will be set by
|
|
|
|
|
|
default, it is helpful for large sized SMR or ZNS devices to
|
|
|
|
|
|
reduce memory cost by getting rid of fs metadata supports small
|
|
|
|
|
|
discard.
|
2022-06-20 17:38:42 +00:00
|
|
|
|
memory=%s Control memory mode. This supports "normal" and "low" modes.
|
|
|
|
|
|
"low" mode is introduced to support low memory devices.
|
|
|
|
|
|
Because of the nature of low memory devices, in this mode, f2fs
|
|
|
|
|
|
will try to save memory sometimes by sacrificing performance.
|
|
|
|
|
|
"normal" mode is the default mode and same as before.
|
2022-12-02 01:37:15 +00:00
|
|
|
|
age_extent_cache Enable an age extent cache based on rb-tree. It records
|
|
|
|
|
|
data block update frequency of the extent per inode, in
|
|
|
|
|
|
order to provide better temperature hints for data block
|
|
|
|
|
|
allocation.
|
2023-04-23 15:49:15 +00:00
|
|
|
|
errors=%s Specify f2fs behavior on critical errors. This supports modes:
|
|
|
|
|
|
"panic", "continue" and "remount-ro", respectively, trigger
|
|
|
|
|
|
panic immediately, continue without doing anything, and remount
|
|
|
|
|
|
the partition in read-only mode. By default it uses "continue"
|
|
|
|
|
|
mode.
|
|
|
|
|
|
====================== =============== =============== ========
|
|
|
|
|
|
mode continue remount-ro panic
|
|
|
|
|
|
====================== =============== =============== ========
|
2023-08-14 21:28:22 +00:00
|
|
|
|
access ops normal normal N/A
|
2023-04-23 15:49:15 +00:00
|
|
|
|
syscall errors -EIO -EROFS N/A
|
|
|
|
|
|
mount option rw ro N/A
|
|
|
|
|
|
pending dir write keep keep N/A
|
|
|
|
|
|
pending non-dir write drop keep N/A
|
|
|
|
|
|
pending node write drop keep N/A
|
|
|
|
|
|
pending meta write keep keep N/A
|
|
|
|
|
|
====================== =============== =============== ========
|
2020-06-22 13:35:39 +00:00
|
|
|
|
======================== ============================================================
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
2020-02-17 16:12:04 +00:00
|
|
|
|
Debugfs Entries
|
|
|
|
|
|
===============
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
|
|
|
|
|
/sys/kernel/debug/f2fs/ contains information about all the partitions mounted as
|
|
|
|
|
|
f2fs. Each file shows the whole f2fs information.
|
|
|
|
|
|
|
|
|
|
|
|
/sys/kernel/debug/f2fs/status includes:
|
2020-02-17 16:12:04 +00:00
|
|
|
|
|
2012-11-02 08:05:42 +00:00
|
|
|
|
- major file system information managed by f2fs currently
|
|
|
|
|
|
- average SIT information about whole segments
|
|
|
|
|
|
- current memory footprint consumed by f2fs.
|
|
|
|
|
|
|
2020-02-17 16:12:04 +00:00
|
|
|
|
Sysfs Entries
|
|
|
|
|
|
=============
|
2013-08-04 14:09:40 +00:00
|
|
|
|
|
2017-02-07 21:08:01 +00:00
|
|
|
|
Information about mounted f2fs file systems can be found in
|
2013-08-04 14:09:40 +00:00
|
|
|
|
/sys/fs/f2fs. Each mounted filesystem will have a directory in
|
|
|
|
|
|
/sys/fs/f2fs based on its device name (i.e., /sys/fs/f2fs/sda).
|
|
|
|
|
|
The files in each per-device directory are shown in table below.
|
|
|
|
|
|
|
|
|
|
|
|
Files in /sys/fs/f2fs/<devname>
|
|
|
|
|
|
(see also Documentation/ABI/testing/sysfs-fs-f2fs)
|
2019-07-23 23:05:28 +00:00
|
|
|
|
|
2020-02-17 16:12:04 +00:00
|
|
|
|
Usage
|
|
|
|
|
|
=====
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
|
|
|
|
|
1. Download userland tools and compile them.
|
|
|
|
|
|
|
|
|
|
|
|
2. Skip, if f2fs was compiled statically inside kernel.
|
2020-02-17 16:12:04 +00:00
|
|
|
|
Otherwise, insert the f2fs.ko module::
|
|
|
|
|
|
|
|
|
|
|
|
# insmod f2fs.ko
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
2020-09-03 00:08:31 +00:00
|
|
|
|
3. Create a directory to use when mounting::
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
2020-02-17 16:12:04 +00:00
|
|
|
|
# mkdir /mnt/f2fs
|
|
|
|
|
|
|
|
|
|
|
|
4. Format the block device, and then mount as f2fs::
|
|
|
|
|
|
|
|
|
|
|
|
# mkfs.f2fs -l label /dev/block_device
|
|
|
|
|
|
# mount -t f2fs /dev/block_device /mnt/f2fs
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
2013-07-04 08:12:47 +00:00
|
|
|
|
mkfs.f2fs
|
|
|
|
|
|
---------
|
|
|
|
|
|
The mkfs.f2fs is for the use of formatting a partition as the f2fs filesystem,
|
|
|
|
|
|
which builds a basic on-disk layout.
|
|
|
|
|
|
|
2020-08-31 17:22:17 +00:00
|
|
|
|
The quick options consist of:
|
2020-02-17 16:12:04 +00:00
|
|
|
|
|
|
|
|
|
|
=============== ===========================================================
|
|
|
|
|
|
``-l [label]`` Give a volume label, up to 512 unicode name.
|
|
|
|
|
|
``-a [0 or 1]`` Split start location of each area for heap-based allocation.
|
|
|
|
|
|
|
|
|
|
|
|
1 is set by default, which performs this.
|
|
|
|
|
|
``-o [int]`` Set overprovision ratio in percent over volume size.
|
|
|
|
|
|
|
|
|
|
|
|
5 is set by default.
|
|
|
|
|
|
``-s [int]`` Set the number of segments per section.
|
|
|
|
|
|
|
|
|
|
|
|
1 is set by default.
|
|
|
|
|
|
``-z [int]`` Set the number of sections per zone.
|
|
|
|
|
|
|
|
|
|
|
|
1 is set by default.
|
|
|
|
|
|
``-e [str]`` Set basic extension list. e.g. "mp3,gif,mov"
|
|
|
|
|
|
``-t [0 or 1]`` Disable discard command or not.
|
|
|
|
|
|
|
|
|
|
|
|
1 is set by default, which conducts discard.
|
|
|
|
|
|
=============== ===========================================================
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
2020-09-03 00:08:31 +00:00
|
|
|
|
Note: please refer to the manpage of mkfs.f2fs(8) to get full option list.
|
2020-08-31 17:22:17 +00:00
|
|
|
|
|
2013-07-04 08:12:47 +00:00
|
|
|
|
fsck.f2fs
|
|
|
|
|
|
---------
|
|
|
|
|
|
The fsck.f2fs is a tool to check the consistency of an f2fs-formatted
|
|
|
|
|
|
partition, which examines whether the filesystem metadata and user-made data
|
|
|
|
|
|
are cross-referenced correctly or not.
|
|
|
|
|
|
Note that, initial version of the tool does not fix any inconsistency.
|
|
|
|
|
|
|
2020-08-31 17:22:17 +00:00
|
|
|
|
The quick options consist of::
|
2020-02-17 16:12:04 +00:00
|
|
|
|
|
2013-07-04 08:12:47 +00:00
|
|
|
|
-d debug level [default:0]
|
|
|
|
|
|
|
2020-09-03 00:08:31 +00:00
|
|
|
|
Note: please refer to the manpage of fsck.f2fs(8) to get full option list.
|
2020-08-31 17:22:17 +00:00
|
|
|
|
|
2013-07-04 08:12:47 +00:00
|
|
|
|
dump.f2fs
|
|
|
|
|
|
---------
|
|
|
|
|
|
The dump.f2fs shows the information of specific inode and dumps SSA and SIT to
|
|
|
|
|
|
file. Each file is dump_ssa and dump_sit.
|
|
|
|
|
|
|
|
|
|
|
|
The dump.f2fs is used to debug on-disk data structures of the f2fs filesystem.
|
2015-11-16 11:46:28 +00:00
|
|
|
|
It shows on-disk inode information recognized by a given inode number, and is
|
2013-07-04 08:12:47 +00:00
|
|
|
|
able to dump all the SSA and SIT entries into predefined files, ./dump_ssa and
|
|
|
|
|
|
./dump_sit respectively.
|
|
|
|
|
|
|
2020-02-17 16:12:04 +00:00
|
|
|
|
The options consist of::
|
|
|
|
|
|
|
2013-07-04 08:12:47 +00:00
|
|
|
|
-d debug level [default:0]
|
|
|
|
|
|
-i inode no (hex)
|
|
|
|
|
|
-s [SIT dump segno from #1~#2 (decimal), for all 0~-1]
|
|
|
|
|
|
-a [SSA dump segno from #1~#2 (decimal), for all 0~-1]
|
|
|
|
|
|
|
2020-02-17 16:12:04 +00:00
|
|
|
|
Examples::
|
|
|
|
|
|
|
|
|
|
|
|
# dump.f2fs -i [ino] /dev/sdx
|
|
|
|
|
|
# dump.f2fs -s 0~-1 /dev/sdx (SIT dump)
|
|
|
|
|
|
# dump.f2fs -a 0~-1 /dev/sdx (SSA dump)
|
2013-07-04 08:12:47 +00:00
|
|
|
|
|
2020-09-03 00:08:31 +00:00
|
|
|
|
Note: please refer to the manpage of dump.f2fs(8) to get full option list.
|
2020-08-31 17:22:17 +00:00
|
|
|
|
|
|
|
|
|
|
sload.f2fs
|
|
|
|
|
|
----------
|
2023-08-14 21:28:22 +00:00
|
|
|
|
The sload.f2fs gives a way to insert files and directories in the existing disk
|
2020-08-31 17:22:17 +00:00
|
|
|
|
image. This tool is useful when building f2fs images given compiled files.
|
|
|
|
|
|
|
2020-09-03 00:08:31 +00:00
|
|
|
|
Note: please refer to the manpage of sload.f2fs(8) to get full option list.
|
2020-08-31 17:22:17 +00:00
|
|
|
|
|
|
|
|
|
|
resize.f2fs
|
|
|
|
|
|
-----------
|
2020-09-03 00:08:31 +00:00
|
|
|
|
The resize.f2fs lets a user resize the f2fs-formatted disk image, while preserving
|
2020-08-31 17:22:17 +00:00
|
|
|
|
all the files and directories stored in the image.
|
|
|
|
|
|
|
2020-09-03 00:08:31 +00:00
|
|
|
|
Note: please refer to the manpage of resize.f2fs(8) to get full option list.
|
2020-08-31 17:22:17 +00:00
|
|
|
|
|
|
|
|
|
|
defrag.f2fs
|
|
|
|
|
|
-----------
|
2020-09-03 00:08:31 +00:00
|
|
|
|
The defrag.f2fs can be used to defragment scattered written data as well as
|
2020-08-31 17:22:17 +00:00
|
|
|
|
filesystem metadata across the disk. This can improve the write speed by giving
|
|
|
|
|
|
more free consecutive space.
|
|
|
|
|
|
|
2020-09-03 00:08:31 +00:00
|
|
|
|
Note: please refer to the manpage of defrag.f2fs(8) to get full option list.
|
2020-08-31 17:22:17 +00:00
|
|
|
|
|
|
|
|
|
|
f2fs_io
|
|
|
|
|
|
-------
|
|
|
|
|
|
The f2fs_io is a simple tool to issue various filesystem APIs as well as
|
|
|
|
|
|
f2fs-specific ones, which is very useful for QA tests.
|
|
|
|
|
|
|
2020-09-03 00:08:31 +00:00
|
|
|
|
Note: please refer to the manpage of f2fs_io(8) to get full option list.
|
2020-08-31 17:22:17 +00:00
|
|
|
|
|
2020-02-17 16:12:04 +00:00
|
|
|
|
Design
|
|
|
|
|
|
======
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
|
|
|
|
|
On-disk Layout
|
|
|
|
|
|
--------------
|
|
|
|
|
|
|
|
|
|
|
|
F2FS divides the whole volume into a number of segments, each of which is fixed
|
|
|
|
|
|
to 2MB in size. A section is composed of consecutive segments, and a zone
|
|
|
|
|
|
consists of a set of sections. By default, section and zone sizes are set to one
|
|
|
|
|
|
segment size identically, but users can easily modify the sizes by mkfs.
|
|
|
|
|
|
|
|
|
|
|
|
F2FS splits the entire volume into six areas, and all the areas except superblock
|
2020-09-03 00:08:31 +00:00
|
|
|
|
consist of multiple segments as described below::
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
|
|
|
|
|
align with the zone size <-|
|
|
|
|
|
|
|-> align with the segment size
|
|
|
|
|
|
_________________________________________________________________________
|
2012-12-31 05:59:04 +00:00
|
|
|
|
| | | Segment | Node | Segment | |
|
|
|
|
|
|
| Superblock | Checkpoint | Info. | Address | Summary | Main |
|
|
|
|
|
|
| (SB) | (CP) | Table (SIT) | Table (NAT) | Area (SSA) | |
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|____________|_____2______|______N______|______N______|______N_____|__N___|
|
|
|
|
|
|
. .
|
|
|
|
|
|
. .
|
|
|
|
|
|
. .
|
|
|
|
|
|
._________________________________________.
|
|
|
|
|
|
|_Segment_|_..._|_Segment_|_..._|_Segment_|
|
|
|
|
|
|
. .
|
|
|
|
|
|
._________._________
|
|
|
|
|
|
|_section_|__...__|_
|
|
|
|
|
|
. .
|
|
|
|
|
|
.________.
|
|
|
|
|
|
|__zone__|
|
|
|
|
|
|
|
|
|
|
|
|
- Superblock (SB)
|
2020-02-17 16:12:04 +00:00
|
|
|
|
It is located at the beginning of the partition, and there exist two copies
|
2012-11-02 08:05:42 +00:00
|
|
|
|
to avoid file system crash. It contains basic partition information and some
|
|
|
|
|
|
default parameters of f2fs.
|
|
|
|
|
|
|
|
|
|
|
|
- Checkpoint (CP)
|
2020-02-17 16:12:04 +00:00
|
|
|
|
It contains file system information, bitmaps for valid NAT/SIT sets, orphan
|
2012-11-02 08:05:42 +00:00
|
|
|
|
inode lists, and summary entries of current active segments.
|
|
|
|
|
|
|
|
|
|
|
|
- Segment Information Table (SIT)
|
2020-02-17 16:12:04 +00:00
|
|
|
|
It contains segment information such as valid block count and bitmap for the
|
2012-11-02 08:05:42 +00:00
|
|
|
|
validity of all the blocks.
|
|
|
|
|
|
|
2012-12-31 05:59:04 +00:00
|
|
|
|
- Node Address Table (NAT)
|
2020-02-17 16:12:04 +00:00
|
|
|
|
It is composed of a block address table for all the node blocks stored in
|
2012-12-31 05:59:04 +00:00
|
|
|
|
Main area.
|
|
|
|
|
|
|
2012-11-02 08:05:42 +00:00
|
|
|
|
- Segment Summary Area (SSA)
|
2020-02-17 16:12:04 +00:00
|
|
|
|
It contains summary entries which contains the owner information of all the
|
2012-11-02 08:05:42 +00:00
|
|
|
|
data and node blocks stored in Main area.
|
|
|
|
|
|
|
|
|
|
|
|
- Main Area
|
2020-02-17 16:12:04 +00:00
|
|
|
|
It contains file and directory data including their indices.
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
|
|
|
|
|
In order to avoid misalignment between file system and flash-based storage, F2FS
|
|
|
|
|
|
aligns the start block address of CP with the segment size. Also, it aligns the
|
|
|
|
|
|
start block address of Main area with the zone size by reserving some segments
|
|
|
|
|
|
in SSA area.
|
|
|
|
|
|
|
|
|
|
|
|
Reference the following survey for additional technical details.
|
|
|
|
|
|
https://wiki.linaro.org/WorkingGroups/Kernel/Projects/FlashCardSurvey
|
|
|
|
|
|
|
|
|
|
|
|
File System Metadata Structure
|
|
|
|
|
|
------------------------------
|
|
|
|
|
|
|
|
|
|
|
|
F2FS adopts the checkpointing scheme to maintain file system consistency. At
|
|
|
|
|
|
mount time, F2FS first tries to find the last valid checkpoint data by scanning
|
|
|
|
|
|
CP area. In order to reduce the scanning time, F2FS uses only two copies of CP.
|
|
|
|
|
|
One of them always indicates the last valid data, which is called as shadow copy
|
|
|
|
|
|
mechanism. In addition to CP, NAT and SIT also adopt the shadow copy mechanism.
|
|
|
|
|
|
|
|
|
|
|
|
For file system consistency, each CP points to which NAT and SIT copies are
|
2020-02-17 16:12:04 +00:00
|
|
|
|
valid, as shown as below::
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
|
|
|
|
|
+--------+----------+---------+
|
2012-12-31 05:59:04 +00:00
|
|
|
|
| CP | SIT | NAT |
|
2012-11-02 08:05:42 +00:00
|
|
|
|
+--------+----------+---------+
|
|
|
|
|
|
. . . .
|
|
|
|
|
|
. . . .
|
|
|
|
|
|
. . . .
|
|
|
|
|
|
+-------+-------+--------+--------+--------+--------+
|
2012-12-31 05:59:04 +00:00
|
|
|
|
| CP #0 | CP #1 | SIT #0 | SIT #1 | NAT #0 | NAT #1 |
|
2012-11-02 08:05:42 +00:00
|
|
|
|
+-------+-------+--------+--------+--------+--------+
|
|
|
|
|
|
| ^ ^
|
|
|
|
|
|
| | |
|
|
|
|
|
|
`----------------------------------------'
|
|
|
|
|
|
|
|
|
|
|
|
Index Structure
|
|
|
|
|
|
---------------
|
|
|
|
|
|
|
|
|
|
|
|
The key data structure to manage the data locations is a "node". Similar to
|
|
|
|
|
|
traditional file structures, F2FS has three types of node: inode, direct node,
|
2012-12-05 08:45:32 +00:00
|
|
|
|
indirect node. F2FS assigns 4KB to an inode block which contains 923 data block
|
2012-11-02 08:05:42 +00:00
|
|
|
|
indices, two direct node pointers, two indirect node pointers, and one double
|
|
|
|
|
|
indirect node pointer as described below. One direct node block contains 1018
|
|
|
|
|
|
data blocks, and one indirect node block contains also 1018 node blocks. Thus,
|
2020-02-17 16:12:04 +00:00
|
|
|
|
one inode block (i.e., a file) covers::
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
|
|
|
|
|
4KB * (923 + 2 * 1018 + 2 * 1018 * 1018 + 1018 * 1018 * 1018) := 3.94TB.
|
|
|
|
|
|
|
|
|
|
|
|
Inode block (4KB)
|
|
|
|
|
|
|- data (923)
|
|
|
|
|
|
|- direct node (2)
|
|
|
|
|
|
| `- data (1018)
|
|
|
|
|
|
|- indirect node (2)
|
|
|
|
|
|
| `- direct node (1018)
|
|
|
|
|
|
| `- data (1018)
|
|
|
|
|
|
`- double indirect node (1)
|
|
|
|
|
|
`- indirect node (1018)
|
|
|
|
|
|
`- direct node (1018)
|
|
|
|
|
|
`- data (1018)
|
|
|
|
|
|
|
2020-09-03 00:08:31 +00:00
|
|
|
|
Note that all the node blocks are mapped by NAT which means the location of
|
2012-11-02 08:05:42 +00:00
|
|
|
|
each node is translated by the NAT table. In the consideration of the wandering
|
|
|
|
|
|
tree problem, F2FS is able to cut off the propagation of node updates caused by
|
|
|
|
|
|
leaf data writes.
|
|
|
|
|
|
|
|
|
|
|
|
Directory Structure
|
|
|
|
|
|
-------------------
|
|
|
|
|
|
|
|
|
|
|
|
A directory entry occupies 11 bytes, which consists of the following attributes.
|
|
|
|
|
|
|
|
|
|
|
|
- hash hash value of the file name
|
|
|
|
|
|
- ino inode number
|
|
|
|
|
|
- len the length of file name
|
|
|
|
|
|
- type file type such as directory, symlink, etc
|
|
|
|
|
|
|
|
|
|
|
|
A dentry block consists of 214 dentry slots and file names. Therein a bitmap is
|
|
|
|
|
|
used to represent whether each dentry is valid or not. A dentry block occupies
|
|
|
|
|
|
4KB with the following composition.
|
|
|
|
|
|
|
2020-02-17 16:12:04 +00:00
|
|
|
|
::
|
|
|
|
|
|
|
2012-11-02 08:05:42 +00:00
|
|
|
|
Dentry Block(4 K) = bitmap (27 bytes) + reserved (3 bytes) +
|
|
|
|
|
|
dentries(11 * 214 bytes) + file name (8 * 214 bytes)
|
|
|
|
|
|
|
|
|
|
|
|
[Bucket]
|
|
|
|
|
|
+--------------------------------+
|
|
|
|
|
|
|dentry block 1 | dentry block 2 |
|
|
|
|
|
|
+--------------------------------+
|
|
|
|
|
|
. .
|
|
|
|
|
|
. .
|
|
|
|
|
|
. [Dentry Block Structure: 4KB] .
|
|
|
|
|
|
+--------+----------+----------+------------+
|
|
|
|
|
|
| bitmap | reserved | dentries | file names |
|
|
|
|
|
|
+--------+----------+----------+------------+
|
|
|
|
|
|
[Dentry Block: 4KB] . .
|
|
|
|
|
|
. .
|
|
|
|
|
|
. .
|
|
|
|
|
|
+------+------+-----+------+
|
|
|
|
|
|
| hash | ino | len | type |
|
|
|
|
|
|
+------+------+-----+------+
|
|
|
|
|
|
[Dentry Structure: 11 bytes]
|
|
|
|
|
|
|
|
|
|
|
|
F2FS implements multi-level hash tables for directory structure. Each level has
|
|
|
|
|
|
a hash table with dedicated number of hash buckets as shown below. Note that
|
|
|
|
|
|
"A(2B)" means a bucket includes 2 data blocks.
|
|
|
|
|
|
|
2020-02-17 16:12:04 +00:00
|
|
|
|
::
|
|
|
|
|
|
|
|
|
|
|
|
----------------------
|
|
|
|
|
|
A : bucket
|
|
|
|
|
|
B : block
|
|
|
|
|
|
N : MAX_DIR_HASH_DEPTH
|
|
|
|
|
|
----------------------
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
2020-02-17 16:12:04 +00:00
|
|
|
|
level #0 | A(2B)
|
|
|
|
|
|
|
|
|
|
|
|
|
level #1 | A(2B) - A(2B)
|
|
|
|
|
|
|
|
|
|
|
|
|
level #2 | A(2B) - A(2B) - A(2B) - A(2B)
|
|
|
|
|
|
. | . . . .
|
|
|
|
|
|
level #N/2 | A(2B) - A(2B) - A(2B) - A(2B) - A(2B) - ... - A(2B)
|
|
|
|
|
|
. | . . . .
|
|
|
|
|
|
level #N | A(4B) - A(4B) - A(4B) - A(4B) - A(4B) - ... - A(4B)
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
2020-02-17 16:12:04 +00:00
|
|
|
|
The number of blocks and buckets are determined by::
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
|
|
|
|
|
,- 2, if n < MAX_DIR_HASH_DEPTH / 2,
|
|
|
|
|
|
# of blocks in level #n = |
|
|
|
|
|
|
`- 4, Otherwise
|
|
|
|
|
|
|
2014-05-28 00:56:09 +00:00
|
|
|
|
,- 2^(n + dir_level),
|
|
|
|
|
|
| if n + dir_level < MAX_DIR_HASH_DEPTH / 2,
|
2012-11-02 08:05:42 +00:00
|
|
|
|
# of buckets in level #n = |
|
2014-05-28 00:56:09 +00:00
|
|
|
|
`- 2^((MAX_DIR_HASH_DEPTH / 2) - 1),
|
|
|
|
|
|
Otherwise
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
|
|
|
|
|
When F2FS finds a file name in a directory, at first a hash value of the file
|
|
|
|
|
|
name is calculated. Then, F2FS scans the hash table in level #0 to find the
|
|
|
|
|
|
dentry consisting of the file name and its inode number. If not found, F2FS
|
|
|
|
|
|
scans the next hash table in level #1. In this way, F2FS scans hash tables in
|
2020-09-03 00:08:31 +00:00
|
|
|
|
each levels incrementally from 1 to N. In each level F2FS needs to scan only
|
2012-11-02 08:05:42 +00:00
|
|
|
|
one bucket determined by the following equation, which shows O(log(# of files))
|
2020-02-17 16:12:04 +00:00
|
|
|
|
complexity::
|
2012-11-02 08:05:42 +00:00
|
|
|
|
|
|
|
|
|
|
bucket number to scan in level #n = (hash value) % (# of buckets in level #n)
|
|
|
|
|
|
|
|
|
|
|
|
In the case of file creation, F2FS finds empty consecutive slots that cover the
|
|
|
|
|
|
file name. F2FS searches the empty slots in the hash tables of whole levels from
|
|
|
|
|
|
1 to N in the same way as the lookup operation.
|
|
|
|
|
|
|
2020-02-17 16:12:04 +00:00
|
|
|
|
The following figure shows an example of two cases holding children::
|
|
|
|
|
|
|
2012-11-02 08:05:42 +00:00
|
|
|
|
--------------> Dir <--------------
|
|
|
|
|
|
| |
|
|
|
|
|
|
child child
|
|
|
|
|
|
|
|
|
|
|
|
child - child [hole] - child
|
|
|
|
|
|
|
|
|
|
|
|
child - child - child [hole] - [hole] - child
|
|
|
|
|
|
|
|
|
|
|
|
Case 1: Case 2:
|
|
|
|
|
|
Number of children = 6, Number of children = 3,
|
|
|
|
|
|
File size = 7 File size = 7
|
|
|
|
|
|
|
|
|
|
|
|
Default Block Allocation
|
|
|
|
|
|
------------------------
|
|
|
|
|
|
|
|
|
|
|
|
At runtime, F2FS manages six active logs inside "Main" area: Hot/Warm/Cold node
|
|
|
|
|
|
and Hot/Warm/Cold data.
|
|
|
|
|
|
|
|
|
|
|
|
- Hot node contains direct node blocks of directories.
|
|
|
|
|
|
- Warm node contains direct node blocks except hot node blocks.
|
|
|
|
|
|
- Cold node contains indirect node blocks
|
|
|
|
|
|
- Hot data contains dentry blocks
|
|
|
|
|
|
- Warm data contains data blocks except hot and cold data blocks
|
|
|
|
|
|
- Cold data contains multimedia data or migrated data blocks
|
|
|
|
|
|
|
|
|
|
|
|
LFS has two schemes for free space management: threaded log and copy-and-compac-
|
|
|
|
|
|
tion. The copy-and-compaction scheme which is known as cleaning, is well-suited
|
|
|
|
|
|
for devices showing very good sequential write performance, since free segments
|
|
|
|
|
|
are served all the time for writing new data. However, it suffers from cleaning
|
|
|
|
|
|
overhead under high utilization. Contrarily, the threaded log scheme suffers
|
|
|
|
|
|
from random writes, but no cleaning process is needed. F2FS adopts a hybrid
|
|
|
|
|
|
scheme where the copy-and-compaction scheme is adopted by default, but the
|
|
|
|
|
|
policy is dynamically changed to the threaded log scheme according to the file
|
|
|
|
|
|
system status.
|
|
|
|
|
|
|
|
|
|
|
|
In order to align F2FS with underlying flash-based storage, F2FS allocates a
|
|
|
|
|
|
segment in a unit of section. F2FS expects that the section size would be the
|
|
|
|
|
|
same as the unit size of garbage collection in FTL. Furthermore, with respect
|
|
|
|
|
|
to the mapping granularity in FTL, F2FS allocates each section of the active
|
|
|
|
|
|
logs from different zones as much as possible, since FTL can write the data in
|
|
|
|
|
|
the active logs into one allocation unit according to its mapping granularity.
|
|
|
|
|
|
|
|
|
|
|
|
Cleaning process
|
|
|
|
|
|
----------------
|
|
|
|
|
|
|
|
|
|
|
|
F2FS does cleaning both on demand and in the background. On-demand cleaning is
|
|
|
|
|
|
triggered when there are not enough free segments to serve VFS calls. Background
|
|
|
|
|
|
cleaner is operated by a kernel thread, and triggers the cleaning job when the
|
|
|
|
|
|
system is idle.
|
|
|
|
|
|
|
|
|
|
|
|
F2FS supports two victim selection policies: greedy and cost-benefit algorithms.
|
|
|
|
|
|
In the greedy algorithm, F2FS selects a victim segment having the smallest number
|
|
|
|
|
|
of valid blocks. In the cost-benefit algorithm, F2FS selects a victim segment
|
|
|
|
|
|
according to the segment age and the number of valid blocks in order to address
|
|
|
|
|
|
log block thrashing problem in the greedy algorithm. F2FS adopts the greedy
|
|
|
|
|
|
algorithm for on-demand cleaner, while background cleaner adopts cost-benefit
|
|
|
|
|
|
algorithm.
|
|
|
|
|
|
|
|
|
|
|
|
In order to identify whether the data in the victim segment are valid or not,
|
|
|
|
|
|
F2FS manages a bitmap. Each bit represents the validity of a block, and the
|
|
|
|
|
|
bitmap is composed of a bit stream covering whole blocks in main area.
|
2018-01-31 02:36:59 +00:00
|
|
|
|
|
2024-04-17 20:01:55 +00:00
|
|
|
|
Write-hint Policy
|
|
|
|
|
|
-----------------
|
|
|
|
|
|
|
|
|
|
|
|
F2FS sets the whint all the time with the below policy.
|
|
|
|
|
|
|
|
|
|
|
|
===================== ======================== ===================
|
|
|
|
|
|
User F2FS Block
|
|
|
|
|
|
===================== ======================== ===================
|
|
|
|
|
|
N/A META WRITE_LIFE_NONE|REQ_META
|
|
|
|
|
|
N/A HOT_NODE WRITE_LIFE_NONE
|
|
|
|
|
|
N/A WARM_NODE WRITE_LIFE_MEDIUM
|
|
|
|
|
|
N/A COLD_NODE WRITE_LIFE_LONG
|
|
|
|
|
|
ioctl(COLD) COLD_DATA WRITE_LIFE_EXTREME
|
|
|
|
|
|
extension list " "
|
|
|
|
|
|
|
|
|
|
|
|
-- buffered io
|
|
|
|
|
|
N/A COLD_DATA WRITE_LIFE_EXTREME
|
|
|
|
|
|
N/A HOT_DATA WRITE_LIFE_SHORT
|
|
|
|
|
|
N/A WARM_DATA WRITE_LIFE_NOT_SET
|
|
|
|
|
|
|
|
|
|
|
|
-- direct io
|
|
|
|
|
|
WRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME
|
|
|
|
|
|
WRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT
|
|
|
|
|
|
WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET
|
|
|
|
|
|
WRITE_LIFE_NONE " WRITE_LIFE_NONE
|
|
|
|
|
|
WRITE_LIFE_MEDIUM " WRITE_LIFE_MEDIUM
|
|
|
|
|
|
WRITE_LIFE_LONG " WRITE_LIFE_LONG
|
|
|
|
|
|
===================== ======================== ===================
|
|
|
|
|
|
|
2019-06-27 01:23:05 +00:00
|
|
|
|
Fallocate(2) Policy
|
|
|
|
|
|
-------------------
|
|
|
|
|
|
|
2020-09-03 00:08:31 +00:00
|
|
|
|
The default policy follows the below POSIX rule.
|
2019-06-27 01:23:05 +00:00
|
|
|
|
|
|
|
|
|
|
Allocating disk space
|
|
|
|
|
|
The default operation (i.e., mode is zero) of fallocate() allocates
|
|
|
|
|
|
the disk space within the range specified by offset and len. The
|
|
|
|
|
|
file size (as reported by stat(2)) will be changed if offset+len is
|
|
|
|
|
|
greater than the file size. Any subregion within the range specified
|
|
|
|
|
|
by offset and len that did not contain data before the call will be
|
|
|
|
|
|
initialized to zero. This default behavior closely resembles the
|
|
|
|
|
|
behavior of the posix_fallocate(3) library function, and is intended
|
|
|
|
|
|
as a method of optimally implementing that function.
|
|
|
|
|
|
|
|
|
|
|
|
However, once F2FS receives ioctl(fd, F2FS_IOC_SET_PIN_FILE) in prior to
|
2023-08-14 21:28:22 +00:00
|
|
|
|
fallocate(fd, DEFAULT_MODE), it allocates on-disk block addresses having
|
2019-06-27 01:23:05 +00:00
|
|
|
|
zero or random data, which is useful to the below scenario where:
|
2020-02-17 16:12:04 +00:00
|
|
|
|
|
2019-06-27 01:23:05 +00:00
|
|
|
|
1. create(fd)
|
|
|
|
|
|
2. ioctl(fd, F2FS_IOC_SET_PIN_FILE)
|
|
|
|
|
|
3. fallocate(fd, 0, 0, size)
|
|
|
|
|
|
4. address = fibmap(fd, offset)
|
|
|
|
|
|
5. open(blkdev)
|
|
|
|
|
|
6. write(blkdev, address)
|
f2fs: support data compression
This patch tries to support compression in f2fs.
- New term named cluster is defined as basic unit of compression, file can
be divided into multiple clusters logically. One cluster includes 4 << n
(n >= 0) logical pages, compression size is also cluster size, each of
cluster can be compressed or not.
- In cluster metadata layout, one special flag is used to indicate cluster
is compressed one or normal one, for compressed cluster, following metadata
maps cluster to [1, 4 << n - 1] physical blocks, in where f2fs stores
data including compress header and compressed data.
- In order to eliminate write amplification during overwrite, F2FS only
support compression on write-once file, data can be compressed only when
all logical blocks in file are valid and cluster compress ratio is lower
than specified threshold.
- To enable compression on regular inode, there are three ways:
* chattr +c file
* chattr +c dir; touch dir/file
* mount w/ -o compress_extension=ext; touch file.ext
Compress metadata layout:
[Dnode Structure]
+-----------------------------------------------+
| cluster 1 | cluster 2 | ......... | cluster N |
+-----------------------------------------------+
. . . .
. . . .
. Compressed Cluster . . Normal Cluster .
+----------+---------+---------+---------+ +---------+---------+---------+---------+
|compr flag| block 1 | block 2 | block 3 | | block 1 | block 2 | block 3 | block 4 |
+----------+---------+---------+---------+ +---------+---------+---------+---------+
. .
. .
. .
+-------------+-------------+----------+----------------------------+
| data length | data chksum | reserved | compressed data |
+-------------+-------------+----------+----------------------------+
Changelog:
20190326:
- fix error handling of read_end_io().
- remove unneeded comments in f2fs_encrypt_one_page().
20190327:
- fix wrong use of f2fs_cluster_is_full() in f2fs_mpage_readpages().
- don't jump into loop directly to avoid uninitialized variables.
- add TODO tag in error path of f2fs_write_cache_pages().
20190328:
- fix wrong merge condition in f2fs_read_multi_pages().
- check compressed file in f2fs_post_read_required().
20190401
- allow overwrite on non-compressed cluster.
- check cluster meta before writing compressed data.
20190402
- don't preallocate blocks for compressed file.
- add lz4 compress algorithm
- process multiple post read works in one workqueue
Now f2fs supports processing post read work in multiple workqueue,
it shows low performance due to schedule overhead of multiple
workqueue executing orderly.
20190921
- compress: support buffered overwrite
C: compress cluster flag
V: valid block address
N: NEW_ADDR
One cluster contain 4 blocks
before overwrite after overwrite
- VVVV -> CVNN
- CVNN -> VVVV
- CVNN -> CVNN
- CVNN -> CVVV
- CVVV -> CVNN
- CVVV -> CVVV
20191029
- add kconfig F2FS_FS_COMPRESSION to isolate compression related
codes, add kconfig F2FS_FS_{LZO,LZ4} to cover backend algorithm.
note that: will remove lzo backend if Jaegeuk agreed that too.
- update codes according to Eric's comments.
20191101
- apply fixes from Jaegeuk
20191113
- apply fixes from Jaegeuk
- split workqueue for fsverity
20191216
- apply fixes from Jaegeuk
20200117
- fix to avoid NULL pointer dereference
[Jaegeuk Kim]
- add tracepoint for f2fs_{,de}compress_pages()
- fix many bugs and add some compression stats
- fix overwrite/mmap bugs
- address 32bit build error, reported by Geert.
- bug fixes when handling errors and i_compressed_blocks
Reported-by: <noreply@ellerman.id.au>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2019-11-01 10:07:14 +00:00
|
|
|
|
|
|
|
|
|
|
Compression implementation
|
|
|
|
|
|
--------------------------
|
|
|
|
|
|
|
|
|
|
|
|
- New term named cluster is defined as basic unit of compression, file can
|
2020-02-17 16:12:04 +00:00
|
|
|
|
be divided into multiple clusters logically. One cluster includes 4 << n
|
|
|
|
|
|
(n >= 0) logical pages, compression size is also cluster size, each of
|
|
|
|
|
|
cluster can be compressed or not.
|
f2fs: support data compression
This patch tries to support compression in f2fs.
- New term named cluster is defined as basic unit of compression, file can
be divided into multiple clusters logically. One cluster includes 4 << n
(n >= 0) logical pages, compression size is also cluster size, each of
cluster can be compressed or not.
- In cluster metadata layout, one special flag is used to indicate cluster
is compressed one or normal one, for compressed cluster, following metadata
maps cluster to [1, 4 << n - 1] physical blocks, in where f2fs stores
data including compress header and compressed data.
- In order to eliminate write amplification during overwrite, F2FS only
support compression on write-once file, data can be compressed only when
all logical blocks in file are valid and cluster compress ratio is lower
than specified threshold.
- To enable compression on regular inode, there are three ways:
* chattr +c file
* chattr +c dir; touch dir/file
* mount w/ -o compress_extension=ext; touch file.ext
Compress metadata layout:
[Dnode Structure]
+-----------------------------------------------+
| cluster 1 | cluster 2 | ......... | cluster N |
+-----------------------------------------------+
. . . .
. . . .
. Compressed Cluster . . Normal Cluster .
+----------+---------+---------+---------+ +---------+---------+---------+---------+
|compr flag| block 1 | block 2 | block 3 | | block 1 | block 2 | block 3 | block 4 |
+----------+---------+---------+---------+ +---------+---------+---------+---------+
. .
. .
. .
+-------------+-------------+----------+----------------------------+
| data length | data chksum | reserved | compressed data |
+-------------+-------------+----------+----------------------------+
Changelog:
20190326:
- fix error handling of read_end_io().
- remove unneeded comments in f2fs_encrypt_one_page().
20190327:
- fix wrong use of f2fs_cluster_is_full() in f2fs_mpage_readpages().
- don't jump into loop directly to avoid uninitialized variables.
- add TODO tag in error path of f2fs_write_cache_pages().
20190328:
- fix wrong merge condition in f2fs_read_multi_pages().
- check compressed file in f2fs_post_read_required().
20190401
- allow overwrite on non-compressed cluster.
- check cluster meta before writing compressed data.
20190402
- don't preallocate blocks for compressed file.
- add lz4 compress algorithm
- process multiple post read works in one workqueue
Now f2fs supports processing post read work in multiple workqueue,
it shows low performance due to schedule overhead of multiple
workqueue executing orderly.
20190921
- compress: support buffered overwrite
C: compress cluster flag
V: valid block address
N: NEW_ADDR
One cluster contain 4 blocks
before overwrite after overwrite
- VVVV -> CVNN
- CVNN -> VVVV
- CVNN -> CVNN
- CVNN -> CVVV
- CVVV -> CVNN
- CVVV -> CVVV
20191029
- add kconfig F2FS_FS_COMPRESSION to isolate compression related
codes, add kconfig F2FS_FS_{LZO,LZ4} to cover backend algorithm.
note that: will remove lzo backend if Jaegeuk agreed that too.
- update codes according to Eric's comments.
20191101
- apply fixes from Jaegeuk
20191113
- apply fixes from Jaegeuk
- split workqueue for fsverity
20191216
- apply fixes from Jaegeuk
20200117
- fix to avoid NULL pointer dereference
[Jaegeuk Kim]
- add tracepoint for f2fs_{,de}compress_pages()
- fix many bugs and add some compression stats
- fix overwrite/mmap bugs
- address 32bit build error, reported by Geert.
- bug fixes when handling errors and i_compressed_blocks
Reported-by: <noreply@ellerman.id.au>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2019-11-01 10:07:14 +00:00
|
|
|
|
|
|
|
|
|
|
- In cluster metadata layout, one special block address is used to indicate
|
2020-09-03 00:08:31 +00:00
|
|
|
|
a cluster is a compressed one or normal one; for compressed cluster, following
|
2020-02-17 16:12:04 +00:00
|
|
|
|
metadata maps cluster to [1, 4 << n - 1] physical blocks, in where f2fs
|
|
|
|
|
|
stores data including compress header and compressed data.
|
f2fs: support data compression
This patch tries to support compression in f2fs.
- New term named cluster is defined as basic unit of compression, file can
be divided into multiple clusters logically. One cluster includes 4 << n
(n >= 0) logical pages, compression size is also cluster size, each of
cluster can be compressed or not.
- In cluster metadata layout, one special flag is used to indicate cluster
is compressed one or normal one, for compressed cluster, following metadata
maps cluster to [1, 4 << n - 1] physical blocks, in where f2fs stores
data including compress header and compressed data.
- In order to eliminate write amplification during overwrite, F2FS only
support compression on write-once file, data can be compressed only when
all logical blocks in file are valid and cluster compress ratio is lower
than specified threshold.
- To enable compression on regular inode, there are three ways:
* chattr +c file
* chattr +c dir; touch dir/file
* mount w/ -o compress_extension=ext; touch file.ext
Compress metadata layout:
[Dnode Structure]
+-----------------------------------------------+
| cluster 1 | cluster 2 | ......... | cluster N |
+-----------------------------------------------+
. . . .
. . . .
. Compressed Cluster . . Normal Cluster .
+----------+---------+---------+---------+ +---------+---------+---------+---------+
|compr flag| block 1 | block 2 | block 3 | | block 1 | block 2 | block 3 | block 4 |
+----------+---------+---------+---------+ +---------+---------+---------+---------+
. .
. .
. .
+-------------+-------------+----------+----------------------------+
| data length | data chksum | reserved | compressed data |
+-------------+-------------+----------+----------------------------+
Changelog:
20190326:
- fix error handling of read_end_io().
- remove unneeded comments in f2fs_encrypt_one_page().
20190327:
- fix wrong use of f2fs_cluster_is_full() in f2fs_mpage_readpages().
- don't jump into loop directly to avoid uninitialized variables.
- add TODO tag in error path of f2fs_write_cache_pages().
20190328:
- fix wrong merge condition in f2fs_read_multi_pages().
- check compressed file in f2fs_post_read_required().
20190401
- allow overwrite on non-compressed cluster.
- check cluster meta before writing compressed data.
20190402
- don't preallocate blocks for compressed file.
- add lz4 compress algorithm
- process multiple post read works in one workqueue
Now f2fs supports processing post read work in multiple workqueue,
it shows low performance due to schedule overhead of multiple
workqueue executing orderly.
20190921
- compress: support buffered overwrite
C: compress cluster flag
V: valid block address
N: NEW_ADDR
One cluster contain 4 blocks
before overwrite after overwrite
- VVVV -> CVNN
- CVNN -> VVVV
- CVNN -> CVNN
- CVNN -> CVVV
- CVVV -> CVNN
- CVVV -> CVVV
20191029
- add kconfig F2FS_FS_COMPRESSION to isolate compression related
codes, add kconfig F2FS_FS_{LZO,LZ4} to cover backend algorithm.
note that: will remove lzo backend if Jaegeuk agreed that too.
- update codes according to Eric's comments.
20191101
- apply fixes from Jaegeuk
20191113
- apply fixes from Jaegeuk
- split workqueue for fsverity
20191216
- apply fixes from Jaegeuk
20200117
- fix to avoid NULL pointer dereference
[Jaegeuk Kim]
- add tracepoint for f2fs_{,de}compress_pages()
- fix many bugs and add some compression stats
- fix overwrite/mmap bugs
- address 32bit build error, reported by Geert.
- bug fixes when handling errors and i_compressed_blocks
Reported-by: <noreply@ellerman.id.au>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2019-11-01 10:07:14 +00:00
|
|
|
|
|
|
|
|
|
|
- In order to eliminate write amplification during overwrite, F2FS only
|
2020-02-17 16:12:04 +00:00
|
|
|
|
support compression on write-once file, data can be compressed only when
|
2020-07-03 08:39:09 +00:00
|
|
|
|
all logical blocks in cluster contain valid data and compress ratio of
|
|
|
|
|
|
cluster data is lower than specified threshold.
|
f2fs: support data compression
This patch tries to support compression in f2fs.
- New term named cluster is defined as basic unit of compression, file can
be divided into multiple clusters logically. One cluster includes 4 << n
(n >= 0) logical pages, compression size is also cluster size, each of
cluster can be compressed or not.
- In cluster metadata layout, one special flag is used to indicate cluster
is compressed one or normal one, for compressed cluster, following metadata
maps cluster to [1, 4 << n - 1] physical blocks, in where f2fs stores
data including compress header and compressed data.
- In order to eliminate write amplification during overwrite, F2FS only
support compression on write-once file, data can be compressed only when
all logical blocks in file are valid and cluster compress ratio is lower
than specified threshold.
- To enable compression on regular inode, there are three ways:
* chattr +c file
* chattr +c dir; touch dir/file
* mount w/ -o compress_extension=ext; touch file.ext
Compress metadata layout:
[Dnode Structure]
+-----------------------------------------------+
| cluster 1 | cluster 2 | ......... | cluster N |
+-----------------------------------------------+
. . . .
. . . .
. Compressed Cluster . . Normal Cluster .
+----------+---------+---------+---------+ +---------+---------+---------+---------+
|compr flag| block 1 | block 2 | block 3 | | block 1 | block 2 | block 3 | block 4 |
+----------+---------+---------+---------+ +---------+---------+---------+---------+
. .
. .
. .
+-------------+-------------+----------+----------------------------+
| data length | data chksum | reserved | compressed data |
+-------------+-------------+----------+----------------------------+
Changelog:
20190326:
- fix error handling of read_end_io().
- remove unneeded comments in f2fs_encrypt_one_page().
20190327:
- fix wrong use of f2fs_cluster_is_full() in f2fs_mpage_readpages().
- don't jump into loop directly to avoid uninitialized variables.
- add TODO tag in error path of f2fs_write_cache_pages().
20190328:
- fix wrong merge condition in f2fs_read_multi_pages().
- check compressed file in f2fs_post_read_required().
20190401
- allow overwrite on non-compressed cluster.
- check cluster meta before writing compressed data.
20190402
- don't preallocate blocks for compressed file.
- add lz4 compress algorithm
- process multiple post read works in one workqueue
Now f2fs supports processing post read work in multiple workqueue,
it shows low performance due to schedule overhead of multiple
workqueue executing orderly.
20190921
- compress: support buffered overwrite
C: compress cluster flag
V: valid block address
N: NEW_ADDR
One cluster contain 4 blocks
before overwrite after overwrite
- VVVV -> CVNN
- CVNN -> VVVV
- CVNN -> CVNN
- CVNN -> CVVV
- CVVV -> CVNN
- CVVV -> CVVV
20191029
- add kconfig F2FS_FS_COMPRESSION to isolate compression related
codes, add kconfig F2FS_FS_{LZO,LZ4} to cover backend algorithm.
note that: will remove lzo backend if Jaegeuk agreed that too.
- update codes according to Eric's comments.
20191101
- apply fixes from Jaegeuk
20191113
- apply fixes from Jaegeuk
- split workqueue for fsverity
20191216
- apply fixes from Jaegeuk
20200117
- fix to avoid NULL pointer dereference
[Jaegeuk Kim]
- add tracepoint for f2fs_{,de}compress_pages()
- fix many bugs and add some compression stats
- fix overwrite/mmap bugs
- address 32bit build error, reported by Geert.
- bug fixes when handling errors and i_compressed_blocks
Reported-by: <noreply@ellerman.id.au>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2019-11-01 10:07:14 +00:00
|
|
|
|
|
2021-06-08 11:15:08 +00:00
|
|
|
|
- To enable compression on regular inode, there are four ways:
|
2020-02-17 16:12:04 +00:00
|
|
|
|
|
|
|
|
|
|
* chattr +c file
|
|
|
|
|
|
* chattr +c dir; touch dir/file
|
|
|
|
|
|
* mount w/ -o compress_extension=ext; touch file.ext
|
2021-04-13 09:56:53 +00:00
|
|
|
|
* mount w/ -o compress_extension=*; touch any_file
|
|
|
|
|
|
|
2021-06-08 11:15:08 +00:00
|
|
|
|
- To disable compression on regular inode, there are two ways:
|
|
|
|
|
|
|
|
|
|
|
|
* chattr -c file
|
|
|
|
|
|
* mount w/ -o nocompress_extension=ext; touch file.ext
|
|
|
|
|
|
|
|
|
|
|
|
- Priority in between FS_COMPR_FL, FS_NOCOMP_FS, extensions:
|
|
|
|
|
|
|
|
|
|
|
|
* compress_extension=so; nocompress_extension=zip; chattr +c dir; touch
|
|
|
|
|
|
dir/foo.so; touch dir/bar.zip; touch dir/baz.txt; then foo.so and baz.txt
|
|
|
|
|
|
should be compresse, bar.zip should be non-compressed. chattr +c dir/bar.zip
|
|
|
|
|
|
can enable compress on bar.zip.
|
|
|
|
|
|
* compress_extension=so; nocompress_extension=zip; chattr -c dir; touch
|
|
|
|
|
|
dir/foo.so; touch dir/bar.zip; touch dir/baz.txt; then foo.so should be
|
|
|
|
|
|
compresse, bar.zip and baz.txt should be non-compressed.
|
|
|
|
|
|
chattr+c dir/bar.zip; chattr+c dir/baz.txt; can enable compress on bar.zip
|
|
|
|
|
|
and baz.txt.
|
|
|
|
|
|
|
2021-04-13 09:56:53 +00:00
|
|
|
|
- At this point, compression feature doesn't expose compressed space to user
|
|
|
|
|
|
directly in order to guarantee potential data updates later to the space.
|
|
|
|
|
|
Instead, the main goal is to reduce data writes to flash disk as much as
|
|
|
|
|
|
possible, resulting in extending disk life time as well as relaxing IO
|
2021-08-09 02:21:04 +00:00
|
|
|
|
congestion. Alternatively, we've added ioctl(F2FS_IOC_RELEASE_COMPRESS_BLOCKS)
|
2022-06-13 02:08:00 +00:00
|
|
|
|
interface to reclaim compressed space and show it to user after setting a
|
|
|
|
|
|
special flag to the inode. Once the compressed space is released, the flag
|
|
|
|
|
|
will block writing data to the file until either the compressed space is
|
|
|
|
|
|
reserved via ioctl(F2FS_IOC_RESERVE_COMPRESS_BLOCKS) or the file size is
|
|
|
|
|
|
truncated to zero.
|
2020-02-17 16:12:04 +00:00
|
|
|
|
|
|
|
|
|
|
Compress metadata layout::
|
|
|
|
|
|
|
|
|
|
|
|
[Dnode Structure]
|
|
|
|
|
|
+-----------------------------------------------+
|
|
|
|
|
|
| cluster 1 | cluster 2 | ......... | cluster N |
|
|
|
|
|
|
+-----------------------------------------------+
|
|
|
|
|
|
. . . .
|
2022-06-13 02:08:00 +00:00
|
|
|
|
. . . .
|
2020-02-17 16:12:04 +00:00
|
|
|
|
. Compressed Cluster . . Normal Cluster .
|
|
|
|
|
|
+----------+---------+---------+---------+ +---------+---------+---------+---------+
|
|
|
|
|
|
|compr flag| block 1 | block 2 | block 3 | | block 1 | block 2 | block 3 | block 4 |
|
|
|
|
|
|
+----------+---------+---------+---------+ +---------+---------+---------+---------+
|
2022-06-13 02:08:00 +00:00
|
|
|
|
. .
|
2020-02-17 16:12:04 +00:00
|
|
|
|
. .
|
|
|
|
|
|
. .
|
|
|
|
|
|
+-------------+-------------+----------+----------------------------+
|
|
|
|
|
|
| data length | data chksum | reserved | compressed data |
|
|
|
|
|
|
+-------------+-------------+----------+----------------------------+
|
f2fs: support zone capacity less than zone size
NVMe Zoned Namespace devices can have zone-capacity less than zone-size.
Zone-capacity indicates the maximum number of sectors that are usable in
a zone beginning from the first sector of the zone. This makes the sectors
sectors after the zone-capacity till zone-size to be unusable.
This patch set tracks zone-size and zone-capacity in zoned devices and
calculate the usable blocks per segment and usable segments per section.
If zone-capacity is less than zone-size mark only those segments which
start before zone-capacity as free segments. All segments at and beyond
zone-capacity are treated as permanently used segments. In cases where
zone-capacity does not align with segment size the last segment will start
before zone-capacity and end beyond the zone-capacity of the zone. For
such spanning segments only sectors within the zone-capacity are used.
During writes and GC manage the usable segments in a section and usable
blocks per segment. Segments which are beyond zone-capacity are never
allocated, and do not need to be garbage collected, only the segments
which are before zone-capacity needs to garbage collected.
For spanning segments based on the number of usable blocks in that
segment, write to blocks only up to zone-capacity.
Zone-capacity is device specific and cannot be configured by the user.
Since NVMe ZNS device zones are sequentially write only, a block device
with conventional zones or any normal block device is needed along with
the ZNS device for the metadata operations of F2fs.
A typical nvme-cli output of a zoned device shows zone start and capacity
and write pointer as below:
SLBA: 0x0 WP: 0x0 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ
SLBA: 0x20000 WP: 0x20000 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ
SLBA: 0x40000 WP: 0x40000 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ
Here zone size is 64MB, capacity is 49MB, WP is at zone start as the zones
are in EMPTY state. For each zone, only zone start + 49MB is usable area,
any lba/sector after 49MB cannot be read or written to, the drive will fail
any attempts to read/write. So, the second zone starts at 64MB and is
usable till 113MB (64 + 49) and the range between 113 and 128MB is
again unusable. The next zone starts at 128MB, and so on.
Signed-off-by: Aravind Ramesh <aravind.ramesh@wdc.com>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2020-07-16 12:56:56 +00:00
|
|
|
|
|
2020-12-01 04:08:02 +00:00
|
|
|
|
Compression mode
|
|
|
|
|
|
--------------------------
|
|
|
|
|
|
|
|
|
|
|
|
f2fs supports "fs" and "user" compression modes with "compression_mode" mount option.
|
|
|
|
|
|
With this option, f2fs provides a choice to select the way how to compress the
|
|
|
|
|
|
compression enabled files (refer to "Compression implementation" section for how to
|
|
|
|
|
|
enable compression on a regular inode).
|
|
|
|
|
|
|
|
|
|
|
|
1) compress_mode=fs
|
|
|
|
|
|
This is the default option. f2fs does automatic compression in the writeback of the
|
|
|
|
|
|
compression enabled files.
|
|
|
|
|
|
|
|
|
|
|
|
2) compress_mode=user
|
2021-02-04 13:25:56 +00:00
|
|
|
|
This disables the automatic compression and gives the user discretion of choosing the
|
2020-12-01 04:08:02 +00:00
|
|
|
|
target file and the timing. The user can do manual compression/decompression on the
|
|
|
|
|
|
compression enabled files using F2FS_IOC_DECOMPRESS_FILE and F2FS_IOC_COMPRESS_FILE
|
|
|
|
|
|
ioctls like the below.
|
|
|
|
|
|
|
|
|
|
|
|
To decompress a file,
|
|
|
|
|
|
|
|
|
|
|
|
fd = open(filename, O_WRONLY, 0);
|
|
|
|
|
|
ret = ioctl(fd, F2FS_IOC_DECOMPRESS_FILE);
|
|
|
|
|
|
|
|
|
|
|
|
To compress a file,
|
|
|
|
|
|
|
|
|
|
|
|
fd = open(filename, O_WRONLY, 0);
|
|
|
|
|
|
ret = ioctl(fd, F2FS_IOC_COMPRESS_FILE);
|
|
|
|
|
|
|
f2fs: support zone capacity less than zone size
NVMe Zoned Namespace devices can have zone-capacity less than zone-size.
Zone-capacity indicates the maximum number of sectors that are usable in
a zone beginning from the first sector of the zone. This makes the sectors
sectors after the zone-capacity till zone-size to be unusable.
This patch set tracks zone-size and zone-capacity in zoned devices and
calculate the usable blocks per segment and usable segments per section.
If zone-capacity is less than zone-size mark only those segments which
start before zone-capacity as free segments. All segments at and beyond
zone-capacity are treated as permanently used segments. In cases where
zone-capacity does not align with segment size the last segment will start
before zone-capacity and end beyond the zone-capacity of the zone. For
such spanning segments only sectors within the zone-capacity are used.
During writes and GC manage the usable segments in a section and usable
blocks per segment. Segments which are beyond zone-capacity are never
allocated, and do not need to be garbage collected, only the segments
which are before zone-capacity needs to garbage collected.
For spanning segments based on the number of usable blocks in that
segment, write to blocks only up to zone-capacity.
Zone-capacity is device specific and cannot be configured by the user.
Since NVMe ZNS device zones are sequentially write only, a block device
with conventional zones or any normal block device is needed along with
the ZNS device for the metadata operations of F2fs.
A typical nvme-cli output of a zoned device shows zone start and capacity
and write pointer as below:
SLBA: 0x0 WP: 0x0 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ
SLBA: 0x20000 WP: 0x20000 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ
SLBA: 0x40000 WP: 0x40000 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ
Here zone size is 64MB, capacity is 49MB, WP is at zone start as the zones
are in EMPTY state. For each zone, only zone start + 49MB is usable area,
any lba/sector after 49MB cannot be read or written to, the drive will fail
any attempts to read/write. So, the second zone starts at 64MB and is
usable till 113MB (64 + 49) and the range between 113 and 128MB is
again unusable. The next zone starts at 128MB, and so on.
Signed-off-by: Aravind Ramesh <aravind.ramesh@wdc.com>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2020-07-16 12:56:56 +00:00
|
|
|
|
NVMe Zoned Namespace devices
|
|
|
|
|
|
----------------------------
|
|
|
|
|
|
|
|
|
|
|
|
- ZNS defines a per-zone capacity which can be equal or less than the
|
|
|
|
|
|
zone-size. Zone-capacity is the number of usable blocks in the zone.
|
2020-09-03 00:08:31 +00:00
|
|
|
|
F2FS checks if zone-capacity is less than zone-size, if it is, then any
|
f2fs: support zone capacity less than zone size
NVMe Zoned Namespace devices can have zone-capacity less than zone-size.
Zone-capacity indicates the maximum number of sectors that are usable in
a zone beginning from the first sector of the zone. This makes the sectors
sectors after the zone-capacity till zone-size to be unusable.
This patch set tracks zone-size and zone-capacity in zoned devices and
calculate the usable blocks per segment and usable segments per section.
If zone-capacity is less than zone-size mark only those segments which
start before zone-capacity as free segments. All segments at and beyond
zone-capacity are treated as permanently used segments. In cases where
zone-capacity does not align with segment size the last segment will start
before zone-capacity and end beyond the zone-capacity of the zone. For
such spanning segments only sectors within the zone-capacity are used.
During writes and GC manage the usable segments in a section and usable
blocks per segment. Segments which are beyond zone-capacity are never
allocated, and do not need to be garbage collected, only the segments
which are before zone-capacity needs to garbage collected.
For spanning segments based on the number of usable blocks in that
segment, write to blocks only up to zone-capacity.
Zone-capacity is device specific and cannot be configured by the user.
Since NVMe ZNS device zones are sequentially write only, a block device
with conventional zones or any normal block device is needed along with
the ZNS device for the metadata operations of F2fs.
A typical nvme-cli output of a zoned device shows zone start and capacity
and write pointer as below:
SLBA: 0x0 WP: 0x0 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ
SLBA: 0x20000 WP: 0x20000 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ
SLBA: 0x40000 WP: 0x40000 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ
Here zone size is 64MB, capacity is 49MB, WP is at zone start as the zones
are in EMPTY state. For each zone, only zone start + 49MB is usable area,
any lba/sector after 49MB cannot be read or written to, the drive will fail
any attempts to read/write. So, the second zone starts at 64MB and is
usable till 113MB (64 + 49) and the range between 113 and 128MB is
again unusable. The next zone starts at 128MB, and so on.
Signed-off-by: Aravind Ramesh <aravind.ramesh@wdc.com>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2020-07-16 12:56:56 +00:00
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segment which starts after the zone-capacity is marked as not-free in
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the free segment bitmap at initial mount time. These segments are marked
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as permanently used so they are not allocated for writes and
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consequently are not needed to be garbage collected. In case the
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zone-capacity is not aligned to default segment size(2MB), then a segment
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can start before the zone-capacity and span across zone-capacity boundary.
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Such spanning segments are also considered as usable segments. All blocks
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past the zone-capacity are considered unusable in these segments.
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