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![David Howells](/assets/img/avatar_default.png)
Cachefiles has a problem in that it needs to keep the backing file for a cookie open whilst there are local modifications pending that need to be written to it. However, we don't want to keep the file open indefinitely, as that causes EMFILE/ENFILE/ENOMEM problems. Reopening the cache file, however, is a problem if this is being done due to writeback triggered by exit(). Some filesystems will oops if we try to open a file in that context because they want to access current->fs or other resources that have already been dismantled. To get around this, I added the following: (1) An inode flag, I_PINNING_FSCACHE_WB, to be set on a network filesystem inode to indicate that we have a usage count on the cookie caching that inode. (2) A flag in struct writeback_control, unpinned_fscache_wb, that is set when __writeback_single_inode() clears the last dirty page from i_pages - at which point it clears I_PINNING_FSCACHE_WB and sets this flag. This has to be done here so that clearing I_PINNING_FSCACHE_WB can be done atomically with the check of PAGECACHE_TAG_DIRTY that clears I_DIRTY_PAGES. (3) A function, fscache_set_page_dirty(), which if it is not set, sets I_PINNING_FSCACHE_WB and calls fscache_use_cookie() to pin the cache resources. (4) A function, fscache_unpin_writeback(), to be called by ->write_inode() to unuse the cookie. (5) A function, fscache_clear_inode_writeback(), to be called when the inode is evicted, before clear_inode() is called. This cleans up any lingering I_PINNING_FSCACHE_WB. The network filesystem can then use these tools to make sure that fscache_write_to_cache() can write locally modified data to the cache as well as to the server. For the future, I'm working on write helpers for netfs lib that should allow this facility to be removed by keeping track of the dirty regions separately - but that's incomplete at the moment and is also going to be affected by folios, one way or another, since it deals with pages Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/163819615157.215744.17623791756928043114.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906917856.143852.8224898306177154573.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967124567.1823006.14188359004568060298.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/164021524705.640689.17824932021727663017.stgit@warthog.procyon.org.uk/ # v4
405 lines
13 KiB
C
405 lines
13 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* include/linux/writeback.h
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*/
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#ifndef WRITEBACK_H
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#define WRITEBACK_H
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#include <linux/sched.h>
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#include <linux/workqueue.h>
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#include <linux/fs.h>
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#include <linux/flex_proportions.h>
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#include <linux/backing-dev-defs.h>
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#include <linux/blk_types.h>
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struct bio;
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DECLARE_PER_CPU(int, dirty_throttle_leaks);
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/*
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* The 1/4 region under the global dirty thresh is for smooth dirty throttling:
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*
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* (thresh - thresh/DIRTY_FULL_SCOPE, thresh)
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*
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* Further beyond, all dirtier tasks will enter a loop waiting (possibly long
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* time) for the dirty pages to drop, unless written enough pages.
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*
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* The global dirty threshold is normally equal to the global dirty limit,
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* except when the system suddenly allocates a lot of anonymous memory and
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* knocks down the global dirty threshold quickly, in which case the global
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* dirty limit will follow down slowly to prevent livelocking all dirtier tasks.
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*/
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#define DIRTY_SCOPE 8
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#define DIRTY_FULL_SCOPE (DIRTY_SCOPE / 2)
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struct backing_dev_info;
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/*
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* fs/fs-writeback.c
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*/
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enum writeback_sync_modes {
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WB_SYNC_NONE, /* Don't wait on anything */
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WB_SYNC_ALL, /* Wait on every mapping */
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};
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/*
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* A control structure which tells the writeback code what to do. These are
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* always on the stack, and hence need no locking. They are always initialised
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* in a manner such that unspecified fields are set to zero.
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*/
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struct writeback_control {
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long nr_to_write; /* Write this many pages, and decrement
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this for each page written */
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long pages_skipped; /* Pages which were not written */
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/*
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* For a_ops->writepages(): if start or end are non-zero then this is
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* a hint that the filesystem need only write out the pages inside that
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* byterange. The byte at `end' is included in the writeout request.
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*/
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loff_t range_start;
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loff_t range_end;
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enum writeback_sync_modes sync_mode;
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unsigned for_kupdate:1; /* A kupdate writeback */
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unsigned for_background:1; /* A background writeback */
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unsigned tagged_writepages:1; /* tag-and-write to avoid livelock */
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unsigned for_reclaim:1; /* Invoked from the page allocator */
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unsigned range_cyclic:1; /* range_start is cyclic */
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unsigned for_sync:1; /* sync(2) WB_SYNC_ALL writeback */
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unsigned unpinned_fscache_wb:1; /* Cleared I_PINNING_FSCACHE_WB */
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/*
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* When writeback IOs are bounced through async layers, only the
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* initial synchronous phase should be accounted towards inode
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* cgroup ownership arbitration to avoid confusion. Later stages
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* can set the following flag to disable the accounting.
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*/
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unsigned no_cgroup_owner:1;
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unsigned punt_to_cgroup:1; /* cgrp punting, see __REQ_CGROUP_PUNT */
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#ifdef CONFIG_CGROUP_WRITEBACK
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struct bdi_writeback *wb; /* wb this writeback is issued under */
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struct inode *inode; /* inode being written out */
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/* foreign inode detection, see wbc_detach_inode() */
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int wb_id; /* current wb id */
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int wb_lcand_id; /* last foreign candidate wb id */
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int wb_tcand_id; /* this foreign candidate wb id */
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size_t wb_bytes; /* bytes written by current wb */
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size_t wb_lcand_bytes; /* bytes written by last candidate */
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size_t wb_tcand_bytes; /* bytes written by this candidate */
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#endif
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};
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static inline int wbc_to_write_flags(struct writeback_control *wbc)
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{
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int flags = 0;
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if (wbc->punt_to_cgroup)
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flags = REQ_CGROUP_PUNT;
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if (wbc->sync_mode == WB_SYNC_ALL)
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flags |= REQ_SYNC;
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else if (wbc->for_kupdate || wbc->for_background)
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flags |= REQ_BACKGROUND;
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return flags;
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}
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#ifdef CONFIG_CGROUP_WRITEBACK
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#define wbc_blkcg_css(wbc) \
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((wbc)->wb ? (wbc)->wb->blkcg_css : blkcg_root_css)
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#else
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#define wbc_blkcg_css(wbc) (blkcg_root_css)
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#endif /* CONFIG_CGROUP_WRITEBACK */
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/*
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* A wb_domain represents a domain that wb's (bdi_writeback's) belong to
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* and are measured against each other in. There always is one global
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* domain, global_wb_domain, that every wb in the system is a member of.
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* This allows measuring the relative bandwidth of each wb to distribute
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* dirtyable memory accordingly.
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*/
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struct wb_domain {
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spinlock_t lock;
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/*
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* Scale the writeback cache size proportional to the relative
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* writeout speed.
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*
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* We do this by keeping a floating proportion between BDIs, based
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* on page writeback completions [end_page_writeback()]. Those
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* devices that write out pages fastest will get the larger share,
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* while the slower will get a smaller share.
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*
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* We use page writeout completions because we are interested in
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* getting rid of dirty pages. Having them written out is the
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* primary goal.
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*
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* We introduce a concept of time, a period over which we measure
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* these events, because demand can/will vary over time. The length
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* of this period itself is measured in page writeback completions.
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*/
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struct fprop_global completions;
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struct timer_list period_timer; /* timer for aging of completions */
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unsigned long period_time;
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/*
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* The dirtyable memory and dirty threshold could be suddenly
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* knocked down by a large amount (eg. on the startup of KVM in a
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* swapless system). This may throw the system into deep dirty
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* exceeded state and throttle heavy/light dirtiers alike. To
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* retain good responsiveness, maintain global_dirty_limit for
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* tracking slowly down to the knocked down dirty threshold.
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*
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* Both fields are protected by ->lock.
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*/
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unsigned long dirty_limit_tstamp;
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unsigned long dirty_limit;
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};
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/**
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* wb_domain_size_changed - memory available to a wb_domain has changed
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* @dom: wb_domain of interest
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*
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* This function should be called when the amount of memory available to
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* @dom has changed. It resets @dom's dirty limit parameters to prevent
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* the past values which don't match the current configuration from skewing
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* dirty throttling. Without this, when memory size of a wb_domain is
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* greatly reduced, the dirty throttling logic may allow too many pages to
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* be dirtied leading to consecutive unnecessary OOMs and may get stuck in
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* that situation.
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*/
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static inline void wb_domain_size_changed(struct wb_domain *dom)
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{
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spin_lock(&dom->lock);
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dom->dirty_limit_tstamp = jiffies;
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dom->dirty_limit = 0;
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spin_unlock(&dom->lock);
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}
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/*
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* fs/fs-writeback.c
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*/
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struct bdi_writeback;
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void writeback_inodes_sb(struct super_block *, enum wb_reason reason);
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void writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
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enum wb_reason reason);
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void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason);
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void sync_inodes_sb(struct super_block *);
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void wakeup_flusher_threads(enum wb_reason reason);
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void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
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enum wb_reason reason);
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void inode_wait_for_writeback(struct inode *inode);
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void inode_io_list_del(struct inode *inode);
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/* writeback.h requires fs.h; it, too, is not included from here. */
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static inline void wait_on_inode(struct inode *inode)
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{
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might_sleep();
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wait_on_bit(&inode->i_state, __I_NEW, TASK_UNINTERRUPTIBLE);
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}
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#ifdef CONFIG_CGROUP_WRITEBACK
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#include <linux/cgroup.h>
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#include <linux/bio.h>
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void __inode_attach_wb(struct inode *inode, struct page *page);
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void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
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struct inode *inode)
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__releases(&inode->i_lock);
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void wbc_detach_inode(struct writeback_control *wbc);
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void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
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size_t bytes);
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int cgroup_writeback_by_id(u64 bdi_id, int memcg_id,
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enum wb_reason reason, struct wb_completion *done);
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void cgroup_writeback_umount(void);
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bool cleanup_offline_cgwb(struct bdi_writeback *wb);
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/**
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* inode_attach_wb - associate an inode with its wb
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* @inode: inode of interest
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* @page: page being dirtied (may be NULL)
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*
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* If @inode doesn't have its wb, associate it with the wb matching the
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* memcg of @page or, if @page is NULL, %current. May be called w/ or w/o
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* @inode->i_lock.
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*/
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static inline void inode_attach_wb(struct inode *inode, struct page *page)
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{
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if (!inode->i_wb)
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__inode_attach_wb(inode, page);
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}
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/**
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* inode_detach_wb - disassociate an inode from its wb
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* @inode: inode of interest
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*
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* @inode is being freed. Detach from its wb.
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*/
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static inline void inode_detach_wb(struct inode *inode)
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{
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if (inode->i_wb) {
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WARN_ON_ONCE(!(inode->i_state & I_CLEAR));
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wb_put(inode->i_wb);
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inode->i_wb = NULL;
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}
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}
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/**
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* wbc_attach_fdatawrite_inode - associate wbc and inode for fdatawrite
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* @wbc: writeback_control of interest
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* @inode: target inode
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*
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* This function is to be used by __filemap_fdatawrite_range(), which is an
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* alternative entry point into writeback code, and first ensures @inode is
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* associated with a bdi_writeback and attaches it to @wbc.
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*/
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static inline void wbc_attach_fdatawrite_inode(struct writeback_control *wbc,
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struct inode *inode)
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{
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spin_lock(&inode->i_lock);
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inode_attach_wb(inode, NULL);
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wbc_attach_and_unlock_inode(wbc, inode);
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}
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/**
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* wbc_init_bio - writeback specific initializtion of bio
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* @wbc: writeback_control for the writeback in progress
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* @bio: bio to be initialized
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*
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* @bio is a part of the writeback in progress controlled by @wbc. Perform
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* writeback specific initialization. This is used to apply the cgroup
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* writeback context. Must be called after the bio has been associated with
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* a device.
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*/
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static inline void wbc_init_bio(struct writeback_control *wbc, struct bio *bio)
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{
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/*
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* pageout() path doesn't attach @wbc to the inode being written
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* out. This is intentional as we don't want the function to block
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* behind a slow cgroup. Ultimately, we want pageout() to kick off
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* regular writeback instead of writing things out itself.
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*/
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if (wbc->wb)
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bio_associate_blkg_from_css(bio, wbc->wb->blkcg_css);
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}
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#else /* CONFIG_CGROUP_WRITEBACK */
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static inline void inode_attach_wb(struct inode *inode, struct page *page)
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{
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}
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static inline void inode_detach_wb(struct inode *inode)
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{
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}
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static inline void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
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struct inode *inode)
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__releases(&inode->i_lock)
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{
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spin_unlock(&inode->i_lock);
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}
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static inline void wbc_attach_fdatawrite_inode(struct writeback_control *wbc,
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struct inode *inode)
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{
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}
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static inline void wbc_detach_inode(struct writeback_control *wbc)
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{
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}
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static inline void wbc_init_bio(struct writeback_control *wbc, struct bio *bio)
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{
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}
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static inline void wbc_account_cgroup_owner(struct writeback_control *wbc,
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struct page *page, size_t bytes)
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{
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}
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static inline void cgroup_writeback_umount(void)
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{
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}
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#endif /* CONFIG_CGROUP_WRITEBACK */
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/*
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* mm/page-writeback.c
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*/
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void laptop_io_completion(struct backing_dev_info *info);
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void laptop_sync_completion(void);
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void laptop_mode_timer_fn(struct timer_list *t);
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bool node_dirty_ok(struct pglist_data *pgdat);
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int wb_domain_init(struct wb_domain *dom, gfp_t gfp);
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#ifdef CONFIG_CGROUP_WRITEBACK
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void wb_domain_exit(struct wb_domain *dom);
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#endif
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extern struct wb_domain global_wb_domain;
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/* These are exported to sysctl. */
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extern int dirty_background_ratio;
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extern unsigned long dirty_background_bytes;
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extern int vm_dirty_ratio;
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extern unsigned long vm_dirty_bytes;
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extern unsigned int dirty_writeback_interval;
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extern unsigned int dirty_expire_interval;
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extern unsigned int dirtytime_expire_interval;
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extern int vm_highmem_is_dirtyable;
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extern int laptop_mode;
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int dirty_background_ratio_handler(struct ctl_table *table, int write,
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void *buffer, size_t *lenp, loff_t *ppos);
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int dirty_background_bytes_handler(struct ctl_table *table, int write,
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void *buffer, size_t *lenp, loff_t *ppos);
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int dirty_ratio_handler(struct ctl_table *table, int write,
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void *buffer, size_t *lenp, loff_t *ppos);
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int dirty_bytes_handler(struct ctl_table *table, int write,
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void *buffer, size_t *lenp, loff_t *ppos);
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int dirtytime_interval_handler(struct ctl_table *table, int write,
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void *buffer, size_t *lenp, loff_t *ppos);
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int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
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void *buffer, size_t *lenp, loff_t *ppos);
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void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty);
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unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh);
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void wb_update_bandwidth(struct bdi_writeback *wb);
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void balance_dirty_pages_ratelimited(struct address_space *mapping);
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bool wb_over_bg_thresh(struct bdi_writeback *wb);
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typedef int (*writepage_t)(struct page *page, struct writeback_control *wbc,
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void *data);
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int generic_writepages(struct address_space *mapping,
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struct writeback_control *wbc);
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void tag_pages_for_writeback(struct address_space *mapping,
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pgoff_t start, pgoff_t end);
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int write_cache_pages(struct address_space *mapping,
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struct writeback_control *wbc, writepage_t writepage,
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void *data);
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int do_writepages(struct address_space *mapping, struct writeback_control *wbc);
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void writeback_set_ratelimit(void);
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void tag_pages_for_writeback(struct address_space *mapping,
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pgoff_t start, pgoff_t end);
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bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio);
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void folio_account_redirty(struct folio *folio);
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static inline void account_page_redirty(struct page *page)
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{
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folio_account_redirty(page_folio(page));
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}
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bool folio_redirty_for_writepage(struct writeback_control *, struct folio *);
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bool redirty_page_for_writepage(struct writeback_control *, struct page *);
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void sb_mark_inode_writeback(struct inode *inode);
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void sb_clear_inode_writeback(struct inode *inode);
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#endif /* WRITEBACK_H */
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