dm-bufio checks a watermark when it allocates a new buffer in the function __bufio_new. However, it doesn't check the watermark when the user changes the value /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 "max_cache_size_bytes", the watermark will never be checked against the new value because no new buffer would be allocated. This patch changes the function __evict_old_buffers so that it checks the watermark. __evict_old_buffers is called every 30 seconds, so if the user lowes "max_cache_size_bytes", dm-bufio will react to this change within 30 seconds and decrease memory consumption. This patch requires the previous patch "dm-bufio: avoid a possible deadlock due to lock ordering" to be applied. Applying this patch without the previous patch would result in a deadlock. Signed-off-by: Mikulas Patocka <[email protected]> Cc: [email protected] --- drivers/md/dm-bufio.c | 10 ++++++++++ 1 file changed, 10 insertions(+) Index: linux-2.6/drivers/md/dm-bufio.c =================================================================== --- linux-2.6.orig/drivers/md/dm-bufio.c +++ linux-2.6/drivers/md/dm-bufio.c @@ -1835,9 +1835,17 @@ static void __evict_old_buffers(struct d 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) @@ -1862,6 +1870,8 @@ 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); -- dm-devel mailing list [email protected] https://www.redhat.com/mailman/listinfo/dm-devel
