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btrfs: Optimize unallocated chunks discard

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Currently unallocated chunks are always trimmed. For example
2 consecutive trims on large storage would trim freespace twice
irrespective of whether the space was actually allocated or not between
those trims.

Optimise this behavior by exploiting the newly introduced alloc_state
tree of btrfs_device. A new CHUNK_TRIMMED bit is used to mark
those unallocated chunks which have been trimmed and have not been
allocated afterwards. On chunk allocation the respective underlying devices'
physical space will have its CHUNK_TRIMMED flag cleared. This avoids
submitting discards for space which hasn't been changed since the last
time discard was issued.

This applies to the single mount period of the filesystem as the
information is not stored permanently.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Nikolay Borisov
2019-03-27 14:24:16 +02:00
committed by David Sterba
parent e74e3993bc
commit 8811133d8a
3 changed files with 66 additions and 3 deletions
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8
fs/btrfs/extent_io.h
View File

@@ -27,8 +27,14 @@
EXTENT_CLEAR_DATA_RESV)
#define EXTENT_CTLBITS (EXTENT_DO_ACCOUNTING)
/* Redefined bits above which are used only in the device allocation tree */
/*
* Redefined bits above which are used only in the device allocation tree,
* shouldn't be using EXTENT_LOCKED / EXTENT_BOUNDARY / EXTENT_CLEAR_META_RESV
* / EXTENT_CLEAR_DATA_RESV because they have special meaning to the bit
* manipulation functions
*/
#define CHUNK_ALLOCATED EXTENT_DIRTY
#define CHUNK_TRIMMED EXTENT_DEFRAG
/*
* flags for bio submission. The high bits indicate the compression