5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Ming-Hung Tsai <mtsai@xxxxxxxxxx>
commit f484697e619a83ecc370443a34746379ad99d204 upstream.
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@xxxxxxxxxx>
Fixes: f494a9c6b1b6 ("dm cache: cache shrinking support")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Acked-by: Joe Thornber <thornber@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/md/dm-cache-target.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -3009,14 +3009,14 @@ static bool can_resize(struct cache *cac
/*
* 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;
