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sbitmap: optimise sbitmap_deferred_clear()

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Because of spinlocks and atomics sbitmap_deferred_clear() have to reload
&sb->map[index] on each access even though the map address won't change.
Pass in sbitmap_word instead of {sb, index}, so it's cached in a
variable. It also improves code generation of
sbitmap_find_bit_in_index().

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: John Garry <john.garry@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2020-11-22 15:35:45 +00:00 committed by Jens Axboe
parent f6f371f7db
commit b78beea038
1 changed files with 12 additions and 12 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

24
lib/sbitmap.c
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@ -12,32 +12,32 @@
/*
* See if we have deferred clears that we can batch move
*/
static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
static inline bool sbitmap_deferred_clear(struct sbitmap_word *map)
{
unsigned long mask, val;
bool ret = false;
unsigned long flags;
spin_lock_irqsave(&sb->map[index].swap_lock, flags);
spin_lock_irqsave(&map->swap_lock, flags);
if (!sb->map[index].cleared)
if (!map->cleared)
goto out_unlock;
/*
* First get a stable cleared mask, setting the old mask to 0.
*/
mask = xchg(&sb->map[index].cleared, 0);
mask = xchg(&map->cleared, 0);
/*
* Now clear the masked bits in our free word
*/
do {
val = sb->map[index].word;
} while (cmpxchg(&sb->map[index].word, val, val & ~mask) != val);
val = map->word;
} while (cmpxchg(&map->word, val, val & ~mask) != val);
ret = true;
out_unlock:
spin_unlock_irqrestore(&sb->map[index].swap_lock, flags);
spin_unlock_irqrestore(&map->swap_lock, flags);
return ret;
}
@ -92,7 +92,7 @@ void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
unsigned int i;
for (i = 0; i < sb->map_nr; i++)
sbitmap_deferred_clear(sb, i);
sbitmap_deferred_clear(&sb->map[i]);
sb->depth = depth;
sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
@ -139,15 +139,15 @@ static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
static int sbitmap_find_bit_in_index(struct sbitmap *sb, int index,
unsigned int alloc_hint, bool round_robin)
{
struct sbitmap_word *map = &sb->map[index];
int nr;
do {
nr = __sbitmap_get_word(&sb->map[index].word,
sb->map[index].depth, alloc_hint,
nr = __sbitmap_get_word(&map->word, map->depth, alloc_hint,
!round_robin);
if (nr != -1)
break;
if (!sbitmap_deferred_clear(sb, index))
if (!sbitmap_deferred_clear(map))
break;
} while (1);
@ -207,7 +207,7 @@ int sbitmap_get_shallow(struct sbitmap *sb, unsigned int alloc_hint,
break;
}
if (sbitmap_deferred_clear(sb, index))
if (sbitmap_deferred_clear(&sb->map[index]))
goto again;
/* Jump to next index. */