[PATCH 4/5] 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@xxxxxxxxxx>
---
 drivers/md/dm-cache-target.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 1fcd8c5c220e..fa8ef2c32af8 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -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;
-- 
2.47.0





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