ack
On Tue, Oct 22, 2024 at 8:13 AM Ming-Hung Tsai <mtsai@xxxxxxxxxx> wrote:
>
> 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
>
