From 1190dbeaeaa026a4879e675b8556a150c36a7ced Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Mon, 12 Oct 2026 16:07:58 +0200 Subject: [PATCH] dm-bufio: fix non-working memory limit The function evict_old is supposed to loop and evict buffers while the allocated size is above the threshold. However if it hits one bufio client that is empty, it stops and doesn't attempt to scan other clients. This commit fixes it, so that it skips empty clients and retries up to dm_bufio_client_count times. Fixes: 450e8dee51aa ("dm bufio: improve concurrent IO performance") Cc: stable@vger.kernel.org Signed-off-by: Mikulas Patocka Assisted-by: Claude:claude-opus-5 --- drivers/md/dm-bufio.c | 41 +++++++++++++++++++++++++++++++++++++---- 1 file changed, 37 insertions(+), 4 deletions(-) diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c index d58eed96a8ff..edad64654ef6 100644 --- a/drivers/md/dm-bufio.c +++ b/drivers/md/dm-bufio.c @@ -2545,6 +2545,13 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign init_waitqueue_head(&c->free_buffer_wait); c->async_write_error = 0; + /* + * A client with no buffers yet is not holding the oldest buffer in + * the system; leaving this zeroed would claim exactly that and keep + * the client pinned at the front of dm_bufio_all_clients. + */ + c->oldest_buffer = jiffies; + c->dm_io = dm_io_client_create(); if (IS_ERR(c->dm_io)) { r = PTR_ERR(c->dm_io); @@ -2779,9 +2786,23 @@ static unsigned long __evict_a_few(unsigned long nr_buffers) dm_bufio_unlock(c); - if (count) + if (count) { c->oldest_buffer = oldest_buffer; - __insert_client(c); + __insert_client(c); + } else { + /* + * We evicted nothing, so 'oldest_buffer' tells us nothing new + * and the client keeps its old, possibly very stale, value. + * Requeue it at the back rather than by that value, otherwise + * __insert_client() would put it straight back at the front + * and every subsequent call would pop this same client again, + * never reaching any of the others. + * + * This leaves the list slightly out of order, which is fine - + * it is only ever an approximation. + */ + list_add_tail(&c->client_list, &dm_bufio_all_clients); + } return count; } @@ -2806,11 +2827,23 @@ static void evict_old(void) { unsigned long threshold = dm_bufio_cache_size - dm_bufio_cache_size / DM_BUFIO_LOW_WATERMARK_RATIO; + int unproductive = 0; mutex_lock(&dm_bufio_clients_lock); while (dm_bufio_current_allocated > threshold) { - if (!__evict_a_few(64)) - break; + if (__evict_a_few(64)) { + unproductive = 0; + } else { + /* + * This client had nothing to give. Try the others + * before giving up: one idle client, or one whose + * buffers are all held, must not stop us evicting + * from everybody else. Stop once a whole sweep of + * the client list has freed nothing. + */ + if (++unproductive >= dm_bufio_client_count) + break; + } cond_resched(); } mutex_unlock(&dm_bufio_clients_lock);