mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-09-05 10:29:37 +00:00
![Josef Bacik](/assets/img/avatar_default.png)
Inside of FB, as well as some user reports, we've had a consistent problem of occasional ENOSPC transaction aborts. Inside FB we were seeing ~100-200 ENOSPC aborts per day in the fleet, which is a really low occurrence rate given the size of our fleet, but it's not nothing. There are two causes of this particular problem. First is delayed allocation. The reservation system for delalloc assumes that contiguous dirty ranges will result in 1 file extent item. However if there is memory pressure that results in fragmented writeout, or there is fragmentation in the block groups, this won't necessarily be true. Consider the case where we do a single 256MiB write to a file and then close it. We will have 1 reservation for the inode update, the reservations for the checksum updates, and 1 reservation for the file extent item. At some point later we decide to write this entire range out, but we're so fragmented that we break this into 100 different file extents. Since we've already closed the file and are no longer writing to it there's nothing to trigger a refill of the delalloc block rsv to satisfy the 99 new file extent reservations we need. At this point we exhaust our delalloc reservation, and we begin to steal from the global reserve. If you have enough of these cases going in parallel you can easily exhaust the global reserve, get an ENOSPC at btrfs_alloc_tree_block() time, and then abort the transaction. The other case is the delayed refs reserve. The delayed refs reserve updates its size based on outstanding delayed refs and dirty block groups. However we only refill this block reserve when returning excess reservations and when we call btrfs_start_transaction(root, X). We will reserve 2*X credits at transaction start time, and fill in X into the delayed refs reserve to make sure it stays topped off. Generally this works well, but clearly has downsides. If we do a particularly delayed ref heavy operation we may never catch up in our reservations. Additionally running delayed refs generates more delayed refs, and at that point we may be committing the transaction and have no way to trigger a refill of our delayed refs rsv. Then a similar thing occurs with the delalloc reserve. Generally speaking we well over-reserve in all of our block rsvs. If we reserve 1 credit we're usually reserving around 264k of space, but we'll often not use any of that reservation, or use a few blocks of that reservation. We can be reasonably sure that as long as you were able to reserve space up front for your operation you'll be able to find space on disk for that reservation. So introduce a new flushing state, BTRFS_RESERVE_FLUSH_EMERGENCY. This gets used in the case that we've exhausted our reserve and the global reserve. It simply forces a reservation if we have enough actual space on disk to make the reservation, which is almost always the case. This keeps us from hitting ENOSPC aborts in these odd occurrences where we've not kept up with the delayed work. Fixing this in a complete way is going to be relatively complicated and time consuming. This patch is what I discussed with Filipe earlier this year, and what I put into our kernels inside FB. With this patch we're down to 1-2 ENOSPC aborts per week, which is a significant reduction. This is a decent stop gap until we can work out a more wholistic solution to these two corner cases. Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: David Sterba <dsterba@suse.com>
240 lines
7.2 KiB
C
240 lines
7.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
|
|
|
|
#ifndef BTRFS_SPACE_INFO_H
|
|
#define BTRFS_SPACE_INFO_H
|
|
|
|
#include "volumes.h"
|
|
|
|
/*
|
|
* Different levels for to flush space when doing space reservations.
|
|
*
|
|
* The higher the level, the more methods we try to reclaim space.
|
|
*/
|
|
enum btrfs_reserve_flush_enum {
|
|
/* If we are in the transaction, we can't flush anything.*/
|
|
BTRFS_RESERVE_NO_FLUSH,
|
|
|
|
/*
|
|
* Flush space by:
|
|
* - Running delayed inode items
|
|
* - Allocating a new chunk
|
|
*/
|
|
BTRFS_RESERVE_FLUSH_LIMIT,
|
|
|
|
/*
|
|
* Flush space by:
|
|
* - Running delayed inode items
|
|
* - Running delayed refs
|
|
* - Running delalloc and waiting for ordered extents
|
|
* - Allocating a new chunk
|
|
*/
|
|
BTRFS_RESERVE_FLUSH_EVICT,
|
|
|
|
/*
|
|
* Flush space by above mentioned methods and by:
|
|
* - Running delayed iputs
|
|
* - Committing transaction
|
|
*
|
|
* Can be interrupted by a fatal signal.
|
|
*/
|
|
BTRFS_RESERVE_FLUSH_DATA,
|
|
BTRFS_RESERVE_FLUSH_FREE_SPACE_INODE,
|
|
BTRFS_RESERVE_FLUSH_ALL,
|
|
|
|
/*
|
|
* Pretty much the same as FLUSH_ALL, but can also steal space from
|
|
* global rsv.
|
|
*
|
|
* Can be interrupted by a fatal signal.
|
|
*/
|
|
BTRFS_RESERVE_FLUSH_ALL_STEAL,
|
|
|
|
/*
|
|
* This is for btrfs_use_block_rsv only. We have exhausted our block
|
|
* rsv and our global block rsv. This can happen for things like
|
|
* delalloc where we are overwriting a lot of extents with a single
|
|
* extent and didn't reserve enough space. Alternatively it can happen
|
|
* with delalloc where we reserve 1 extents worth for a large extent but
|
|
* fragmentation leads to multiple extents being created. This will
|
|
* give us the reservation in the case of
|
|
*
|
|
* if (num_bytes < (space_info->total_bytes -
|
|
* btrfs_space_info_used(space_info, false))
|
|
*
|
|
* Which ignores bytes_may_use. This is potentially dangerous, but our
|
|
* reservation system is generally pessimistic so is able to absorb this
|
|
* style of mistake.
|
|
*/
|
|
BTRFS_RESERVE_FLUSH_EMERGENCY,
|
|
};
|
|
|
|
enum btrfs_flush_state {
|
|
FLUSH_DELAYED_ITEMS_NR = 1,
|
|
FLUSH_DELAYED_ITEMS = 2,
|
|
FLUSH_DELAYED_REFS_NR = 3,
|
|
FLUSH_DELAYED_REFS = 4,
|
|
FLUSH_DELALLOC = 5,
|
|
FLUSH_DELALLOC_WAIT = 6,
|
|
FLUSH_DELALLOC_FULL = 7,
|
|
ALLOC_CHUNK = 8,
|
|
ALLOC_CHUNK_FORCE = 9,
|
|
RUN_DELAYED_IPUTS = 10,
|
|
COMMIT_TRANS = 11,
|
|
};
|
|
|
|
struct btrfs_space_info {
|
|
spinlock_t lock;
|
|
|
|
u64 total_bytes; /* total bytes in the space,
|
|
this doesn't take mirrors into account */
|
|
u64 bytes_used; /* total bytes used,
|
|
this doesn't take mirrors into account */
|
|
u64 bytes_pinned; /* total bytes pinned, will be freed when the
|
|
transaction finishes */
|
|
u64 bytes_reserved; /* total bytes the allocator has reserved for
|
|
current allocations */
|
|
u64 bytes_may_use; /* number of bytes that may be used for
|
|
delalloc/allocations */
|
|
u64 bytes_readonly; /* total bytes that are read only */
|
|
/* Total bytes in the space, but only accounts active block groups. */
|
|
u64 active_total_bytes;
|
|
u64 bytes_zone_unusable; /* total bytes that are unusable until
|
|
resetting the device zone */
|
|
|
|
u64 max_extent_size; /* This will hold the maximum extent size of
|
|
the space info if we had an ENOSPC in the
|
|
allocator. */
|
|
/* Chunk size in bytes */
|
|
u64 chunk_size;
|
|
|
|
/*
|
|
* Once a block group drops below this threshold (percents) we'll
|
|
* schedule it for reclaim.
|
|
*/
|
|
int bg_reclaim_threshold;
|
|
|
|
int clamp; /* Used to scale our threshold for preemptive
|
|
flushing. The value is >> clamp, so turns
|
|
out to be a 2^clamp divisor. */
|
|
|
|
unsigned int full:1; /* indicates that we cannot allocate any more
|
|
chunks for this space */
|
|
unsigned int chunk_alloc:1; /* set if we are allocating a chunk */
|
|
|
|
unsigned int flush:1; /* set if we are trying to make space */
|
|
|
|
unsigned int force_alloc; /* set if we need to force a chunk
|
|
alloc for this space */
|
|
|
|
u64 disk_used; /* total bytes used on disk */
|
|
u64 disk_total; /* total bytes on disk, takes mirrors into
|
|
account */
|
|
|
|
u64 flags;
|
|
|
|
struct list_head list;
|
|
/* Protected by the spinlock 'lock'. */
|
|
struct list_head ro_bgs;
|
|
struct list_head priority_tickets;
|
|
struct list_head tickets;
|
|
|
|
/*
|
|
* Size of space that needs to be reclaimed in order to satisfy pending
|
|
* tickets
|
|
*/
|
|
u64 reclaim_size;
|
|
|
|
/*
|
|
* tickets_id just indicates the next ticket will be handled, so note
|
|
* it's not stored per ticket.
|
|
*/
|
|
u64 tickets_id;
|
|
|
|
struct rw_semaphore groups_sem;
|
|
/* for block groups in our same type */
|
|
struct list_head block_groups[BTRFS_NR_RAID_TYPES];
|
|
|
|
struct kobject kobj;
|
|
struct kobject *block_group_kobjs[BTRFS_NR_RAID_TYPES];
|
|
};
|
|
|
|
struct reserve_ticket {
|
|
u64 bytes;
|
|
int error;
|
|
bool steal;
|
|
struct list_head list;
|
|
wait_queue_head_t wait;
|
|
};
|
|
|
|
static inline bool btrfs_mixed_space_info(struct btrfs_space_info *space_info)
|
|
{
|
|
return ((space_info->flags & BTRFS_BLOCK_GROUP_METADATA) &&
|
|
(space_info->flags & BTRFS_BLOCK_GROUP_DATA));
|
|
}
|
|
|
|
/*
|
|
*
|
|
* Declare a helper function to detect underflow of various space info members
|
|
*/
|
|
#define DECLARE_SPACE_INFO_UPDATE(name, trace_name) \
|
|
static inline void \
|
|
btrfs_space_info_update_##name(struct btrfs_fs_info *fs_info, \
|
|
struct btrfs_space_info *sinfo, \
|
|
s64 bytes) \
|
|
{ \
|
|
const u64 abs_bytes = (bytes < 0) ? -bytes : bytes; \
|
|
lockdep_assert_held(&sinfo->lock); \
|
|
trace_update_##name(fs_info, sinfo, sinfo->name, bytes); \
|
|
trace_btrfs_space_reservation(fs_info, trace_name, \
|
|
sinfo->flags, abs_bytes, \
|
|
bytes > 0); \
|
|
if (bytes < 0 && sinfo->name < -bytes) { \
|
|
WARN_ON(1); \
|
|
sinfo->name = 0; \
|
|
return; \
|
|
} \
|
|
sinfo->name += bytes; \
|
|
}
|
|
|
|
DECLARE_SPACE_INFO_UPDATE(bytes_may_use, "space_info");
|
|
DECLARE_SPACE_INFO_UPDATE(bytes_pinned, "pinned");
|
|
|
|
int btrfs_init_space_info(struct btrfs_fs_info *fs_info);
|
|
void btrfs_add_bg_to_space_info(struct btrfs_fs_info *info,
|
|
struct btrfs_block_group *block_group);
|
|
void btrfs_update_space_info_chunk_size(struct btrfs_space_info *space_info,
|
|
u64 chunk_size);
|
|
struct btrfs_space_info *btrfs_find_space_info(struct btrfs_fs_info *info,
|
|
u64 flags);
|
|
u64 __pure btrfs_space_info_used(struct btrfs_space_info *s_info,
|
|
bool may_use_included);
|
|
void btrfs_clear_space_info_full(struct btrfs_fs_info *info);
|
|
void btrfs_dump_space_info(struct btrfs_fs_info *fs_info,
|
|
struct btrfs_space_info *info, u64 bytes,
|
|
int dump_block_groups);
|
|
int btrfs_reserve_metadata_bytes(struct btrfs_fs_info *fs_info,
|
|
struct btrfs_block_rsv *block_rsv,
|
|
u64 orig_bytes,
|
|
enum btrfs_reserve_flush_enum flush);
|
|
void btrfs_try_granting_tickets(struct btrfs_fs_info *fs_info,
|
|
struct btrfs_space_info *space_info);
|
|
int btrfs_can_overcommit(struct btrfs_fs_info *fs_info,
|
|
struct btrfs_space_info *space_info, u64 bytes,
|
|
enum btrfs_reserve_flush_enum flush);
|
|
|
|
static inline void btrfs_space_info_free_bytes_may_use(
|
|
struct btrfs_fs_info *fs_info,
|
|
struct btrfs_space_info *space_info,
|
|
u64 num_bytes)
|
|
{
|
|
spin_lock(&space_info->lock);
|
|
btrfs_space_info_update_bytes_may_use(fs_info, space_info, -num_bytes);
|
|
btrfs_try_granting_tickets(fs_info, space_info);
|
|
spin_unlock(&space_info->lock);
|
|
}
|
|
int btrfs_reserve_data_bytes(struct btrfs_fs_info *fs_info, u64 bytes,
|
|
enum btrfs_reserve_flush_enum flush);
|
|
void btrfs_dump_space_info_for_trans_abort(struct btrfs_fs_info *fs_info);
|
|
void btrfs_init_async_reclaim_work(struct btrfs_fs_info *fs_info);
|
|
|
|
#endif /* BTRFS_SPACE_INFO_H */
|