dm bufio: check new buffer allocation watermark every 30 seconds

commit 390020ad2af9ca04844c4f3b1f299ad8746d84c8 upstream.

dm-bufio checks a watermark when it allocates a new buffer in
__bufio_new().  However, it doesn't check the watermark when the user
changes /sys/module/dm_bufio/parameters/max_cache_size_bytes.

This may result in a problem - if the watermark is high enough so that
all possible buffers are allocated and if the user lowers the value of
"max_cache_size_bytes", the watermark will never be checked against the
new value because no new buffer would be allocated.

To fix this, change __evict_old_buffers() so that it checks the
watermark.  __evict_old_buffers() is called every 30 seconds, so if the
user reduces "max_cache_size_bytes", dm-bufio will react to this change
within 30 seconds and decrease memory consumption.

Depends-on: 1b0fb5a5b2 ("dm bufio: avoid a possible ABBA deadlock")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index d0745965f8ec..c805fd9184bf 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -1782,9 +1782,17 @@ static void __evict_old_buffers(struct dm_bufio_client *c, unsigned long age_hz)
         struct dm_buffer *b, *tmp;
         unsigned retain_target = get_retain_buffers(c);
         unsigned count;
+        LIST_HEAD(write_list);
 
         dm_bufio_lock(c);
 
+        __check_watermark(c, &write_list);
+        if (unlikely(!list_empty(&write_list))) {
+                dm_bufio_unlock(c);
+                __flush_write_list(&write_list);
+                dm_bufio_lock(c);
+        }
+
         count = c->n_buffers[LIST_CLEAN] + c->n_buffers[LIST_DIRTY];
         list_for_each_entry_safe_reverse(b, tmp, &c->lru[LIST_CLEAN], lru_list) {
                 if (count <= retain_target)
@@ -1809,6 +1817,8 @@ static void cleanup_old_buffers(void)
 
         mutex_lock(&dm_bufio_clients_lock);
 
+        __cache_size_refresh();
+
         list_for_each_entry(c, &dm_bufio_all_clients, client_list)
                 __evict_old_buffers(c, max_age_hz);