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authorPavel Begunkov <asml.silence@gmail.com>2020-11-22 18:35:46 +0300
committerJens Axboe <axboe@kernel.dk>2020-12-08 03:12:49 +0300
commit661d4f55a79483aee4970a76e3bd9d4cdc74ac79 (patch)
tree2d239a9e27ebd6e016d4c80cca528883ad4bcc5d /lib/sbitmap.c
parentb78beea038a3087df63bba7adaacb476a8ca95af (diff)
downloadlinux-661d4f55a79483aee4970a76e3bd9d4cdc74ac79.tar.xz
sbitmap: remove swap_lock
map->swap_lock protects map->cleared from concurrent modification, however sbitmap_deferred_clear() is already atomically drains it, so it's guaranteed to not loose bits on concurrent sbitmap_deferred_clear(). A one threaded tag heavy test on top of nullbk showed ~1.5% t-put increase, and 3% -> 1% cycle reduction of sbitmap_get() according to perf. Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'lib/sbitmap.c')
-rw-r--r--lib/sbitmap.c14
1 files changed, 3 insertions, 11 deletions
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index c1c8a4e69325..4fd877048ba8 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -15,13 +15,9 @@
static inline bool sbitmap_deferred_clear(struct sbitmap_word *map)
{
unsigned long mask, val;
- bool ret = false;
- unsigned long flags;
- spin_lock_irqsave(&map->swap_lock, flags);
-
- if (!map->cleared)
- goto out_unlock;
+ if (!READ_ONCE(map->cleared))
+ return false;
/*
* First get a stable cleared mask, setting the old mask to 0.
@@ -35,10 +31,7 @@ static inline bool sbitmap_deferred_clear(struct sbitmap_word *map)
val = map->word;
} while (cmpxchg(&map->word, val, val & ~mask) != val);
- ret = true;
-out_unlock:
- spin_unlock_irqrestore(&map->swap_lock, flags);
- return ret;
+ return true;
}
int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
@@ -80,7 +73,6 @@ int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
for (i = 0; i < sb->map_nr; i++) {
sb->map[i].depth = min(depth, bits_per_word);
depth -= sb->map[i].depth;
- spin_lock_init(&sb->map[i].swap_lock);
}
return 0;
}