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btrfs: add comments for btrfs_reserve_flush_enum 

This enum is the interface exposed to developers.

Although we have a detailed comment explaining the whole idea of space
flushing at the beginning of space-info.c, the exposed enum interface
doesn't have any comment.

Some corner cases, like BTRFS_RESERVE_FLUSH_ALL and
BTRFS_RESERVE_FLUSH_ALL_STEAL can be interrupted by fatal signals, are
not explained at all.

So add some simple comments for these enums as a quick reference.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo 2020-07-13 09:03:22 +08:00 committed by David Sterba
parent 44d354abf3
commit fd7fb634d6
1 changed files with 32 additions and 2 deletions
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34
fs/btrfs/ctree.h
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@ -2560,16 +2560,46 @@ int btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
int btrfs_extent_readonly(struct btrfs_fs_info *fs_info, u64 bytenr);
void btrfs_clear_space_info_full(struct btrfs_fs_info *info);
/*
* 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,
/*
* Flushing delalloc may cause deadlock somewhere, in this
* case, use FLUSH LIMIT
* 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
* - Commiting transaction
*
* Can be interruped by fatal signal.
*/
BTRFS_RESERVE_FLUSH_ALL,
/*
* Pretty much the same as FLUSH_ALL, but can also steal space from
* global rsv.
*
* Can be interruped by fatal signal.
*/
BTRFS_RESERVE_FLUSH_ALL_STEAL,
};