linux-kernel - [PATCH 4.11 026/197] dm bufio: check new buffer allocation watermark every 30 seconds

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Date:   Tue, 23 May 2017 22:06:27 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Mikulas Patocka <mpatocka@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH 4.11 026/197] dm bufio: check new buffer allocation watermark every 30 seconds

4.11-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mikulas Patocka <mpatocka@...hat.com>

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@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -1783,9 +1783,17 @@ 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)
@@ -1810,6 +1818,8 @@ 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);