Patch "dm bufio: check new buffer allocation watermark every 30 seconds" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

dm bufio: check new buffer allocation watermark every 30 seconds

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
dm-bufio-check-new-buffer-allocation-watermark-every-30-seconds.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Mikulas Patocka <[email protected]>
Date: Sun, 30 Apr 2017 17:34:53 -0400
Subject: dm bufio: check new buffer allocation watermark every 30 seconds

From: Mikulas Patocka <[email protected]>

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")

---
 drivers/md/dm-bufio.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

@@ -1782,9 +1782,17 @@ 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)

@@ -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);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/dm-bufio-avoid-a-possible-abba-deadlock.patch queue-4.9/dm-cache-metadata-fail-operations-if-fail_io-mode-has-been-established.patch queue-4.9/dm-raid-select-the-kconfig-option-config_md_raid0.patch queue-4.9/dm-bufio-make-the-parameter-retain_bytes-unsigned-long.patch queue-4.9/dm-bufio-check-new-buffer-allocation-watermark-every-30-seconds.patch