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dm cache: optimize dirty bit checking with find_next_bit when resizing

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When shrinking the fast device, dm-cache iteratively searches for a
dirty bit among the cache blocks to be dropped, which is less efficient.
Use find_next_bit instead, as it is twice as fast as the iterative
approach with test_bit.

Signed-off-by: Ming-Hung Tsai <mtsai@redhat.com>
Fixes: f494a9c6b1 ("dm cache: cache shrinking support")
Cc: stable@vger.kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Acked-by: Joe Thornber <thornber@redhat.com>
This commit is contained in:
Ming-Hung Tsai 2024-10-22 15:13:39 +08:00 committed by Mikulas Patocka
parent 7922277197
commit f484697e61
1 changed files with 8 additions and 8 deletions
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16
drivers/md/dm-cache-target.c
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@ -2911,14 +2911,14 @@ static bool can_resize(struct cache *cache, dm_cblock_t new_size)
/*
* We can't drop a dirty block when shrinking the cache.
*/
while (from_cblock(new_size) < from_cblock(cache->cache_size)) {
if (is_dirty(cache, new_size)) {
DMERR("%s: unable to shrink cache; cache block %llu is dirty",
cache_device_name(cache),
(unsigned long long) from_cblock(new_size));
return false;
}
new_size = to_cblock(from_cblock(new_size) + 1);
new_size = to_cblock(find_next_bit(cache->dirty_bitset,
from_cblock(cache->cache_size),
from_cblock(new_size)));
if (new_size != cache->cache_size) {
DMERR("%s: unable to shrink cache; cache block %llu is dirty",
cache_device_name(cache),
(unsigned long long) from_cblock(new_size));
return false;
}
return true;