block-rsv.c | Explore in Territory

// SPDX-License-Identifier: GPL-2.0

#include "misc.h"
#include "ctree.h"
#include "block-rsv.h"
#include "space-info.h"
#include "transaction.h"
#include "block-group.h"
#include "fs.h"
#include "accessors.h"

/*
 * HOW DO BLOCK RESERVES WORK
 *
 *   Think of block_rsv's as buckets for logically grouped metadata
 *   reservations.  Each block_rsv has a ->size and a ->reserved.  ->size is
 *   how large we want our block rsv to be, ->reserved is how much space is
 *   currently reserved for this block reserve.
 *
 *   ->failfast exists for the truncate case, and is described below.
 *
 * NORMAL OPERATION
 *
 *   -> Reserve
 *     Entrance: btrfs_block_rsv_add, btrfs_block_rsv_refill
 *
 *     We call into btrfs_reserve_metadata_bytes() with our bytes, which is
 *     accounted for in space_info->bytes_may_use, and then add the bytes to
 *     ->reserved, and ->size in the case of btrfs_block_rsv_add.
 *
 *     ->size is an over-estimation of how much we may use for a particular
 *     operation.
 *
 *   -> Use
 *     Entrance: btrfs_use_block_rsv
 *
 *     When we do a btrfs_alloc_tree_block() we call into btrfs_use_block_rsv()
 *     to determine the appropriate block_rsv to use, and then verify that
 *     ->reserved has enough space for our tree block allocation.  Once
 *     successful we subtract fs_info->nodesize from ->reserved.
 *
 *   -> Finish
 *     Entrance: btrfs_block_rsv_release
 *
 *     We are finished with our operation, subtract our individual reservation
 *     from ->size, and then subtract ->size from ->reserved and free up the
 *     excess if there is any.
 *
 *     There is some logic here to refill the delayed refs rsv or the global rsv
 *     as needed, otherwise the excess is subtracted from
 *     space_info->bytes_may_use.
 *
 * TYPES OF BLOCK RESERVES
 *
 * BLOCK_RSV_TRANS, BLOCK_RSV_DELOPS, BLOCK_RSV_CHUNK
 *   These behave normally, as described above, just within the confines of the
 *   lifetime of their particular operation (transaction for the whole trans
 *   handle lifetime, for example).
 *
 * BLOCK_RSV_GLOBAL
 *   It is impossible to properly account for all the space that may be required
 *   to make our extent tree updates.  This block reserve acts as an overflow
 *   buffer in case our delayed refs reserve does not reserve enough space to
 *   update the extent tree.
 *
 *   We can steal from this in some cases as well, notably on evict() or
 *   truncate() in order to help users recover from ENOSPC conditions.
 *
 * BLOCK_RSV_DELALLOC
 *   The individual item sizes are determined by the per-inode size
 *   calculations, which are described with the delalloc code.  This is pretty
 *   straightforward, it's just the calculation of ->size encodes a lot of
 *   different items, and thus it gets used when updating inodes, inserting file
 *   extents, and inserting checksums.
 *
 * BLOCK_RSV_DELREFS
 *   We keep a running tally of how many delayed refs we have on the system.
 *   We assume each one of these delayed refs are going to use a full
 *   reservation.  We use the transaction items and pre-reserve space for every
 *   operation, and use this reservation to refill any gap between ->size and
 *   ->reserved that may exist.
 *
 *   From there it's straightforward, removing a delayed ref means we remove its
 *   count from ->size and free up reservations as necessary.  Since this is
 *   the most dynamic block reserve in the system, we will try to refill this
 *   block reserve first with any excess returned by any other block reserve.
 *
 * BLOCK_RSV_EMPTY
 *   This is the fallback block reserve to make us try to reserve space if we
 *   don't have a specific bucket for this allocation.  It is mostly used for
 *   updating the device tree and such, since that is a separate pool we're
 *   content to just reserve space from the space_info on demand.
 *
 * BLOCK_RSV_TEMP
 *   This is used by things like truncate and iput.  We will temporarily
 *   allocate a block reserve, set it to some size, and then truncate bytes
 *   until we have no space left.  With ->failfast set we'll simply return
 *   ENOSPC from btrfs_use_block_rsv() to signal that we need to unwind and try
 *   to make a new reservation.  This is because these operations are
 *   unbounded, so we want to do as much work as we can, and then back off and
 *   re-reserve.
 */

static u64 block_rsv_release_bytes(struct btrfs_fs_info *fs_info,
				    struct btrfs_block_rsv *block_rsv,
				    struct btrfs_block_rsv *dest, u64 num_bytes,
				    u64 *qgroup_to_release_ret)
{ … }

int btrfs_block_rsv_migrate(struct btrfs_block_rsv *src,
			    struct btrfs_block_rsv *dst, u64 num_bytes,
			    bool update_size)
{ … }

void btrfs_init_block_rsv(struct btrfs_block_rsv *rsv, enum btrfs_rsv_type type)
{ … }

void btrfs_init_metadata_block_rsv(struct btrfs_fs_info *fs_info,
				   struct btrfs_block_rsv *rsv,
				   enum btrfs_rsv_type type)
{ … }

struct btrfs_block_rsv *btrfs_alloc_block_rsv(struct btrfs_fs_info *fs_info,
					      enum btrfs_rsv_type type)
{ … }

void btrfs_free_block_rsv(struct btrfs_fs_info *fs_info,
			  struct btrfs_block_rsv *rsv)
{ … }

int btrfs_block_rsv_add(struct btrfs_fs_info *fs_info,
			struct btrfs_block_rsv *block_rsv, u64 num_bytes,
			enum btrfs_reserve_flush_enum flush)
{ … }

int btrfs_block_rsv_check(struct btrfs_block_rsv *block_rsv, int min_percent)
{ … }

int btrfs_block_rsv_refill(struct btrfs_fs_info *fs_info,
			   struct btrfs_block_rsv *block_rsv, u64 num_bytes,
			   enum btrfs_reserve_flush_enum flush)
{ … }

u64 btrfs_block_rsv_release(struct btrfs_fs_info *fs_info,
			    struct btrfs_block_rsv *block_rsv, u64 num_bytes,
			    u64 *qgroup_to_release)
{ … }

int btrfs_block_rsv_use_bytes(struct btrfs_block_rsv *block_rsv, u64 num_bytes)
{ … }

void btrfs_block_rsv_add_bytes(struct btrfs_block_rsv *block_rsv,
			       u64 num_bytes, bool update_size)
{ … }

void btrfs_update_global_block_rsv(struct btrfs_fs_info *fs_info)
{ … }

void btrfs_init_root_block_rsv(struct btrfs_root *root)
{ … }

void btrfs_init_global_block_rsv(struct btrfs_fs_info *fs_info)
{ … }

void btrfs_release_global_block_rsv(struct btrfs_fs_info *fs_info)
{ … }

static struct btrfs_block_rsv *get_block_rsv(
					const struct btrfs_trans_handle *trans,
					const struct btrfs_root *root)
{ … }

struct btrfs_block_rsv *btrfs_use_block_rsv(struct btrfs_trans_handle *trans,
					    struct btrfs_root *root,
					    u32 blocksize)
{ … }

int btrfs_check_trunc_cache_free_space(struct btrfs_fs_info *fs_info,
				       struct btrfs_block_rsv *rsv)
{ … }
linux/fs/btrfs/block-rsv.c
