dm writecache: set a default MAX_WRITEBACK_JOBS

[ Upstream commit ca7dc242e358e46d963b32f9d9dd829785a9e957 ]

dm-writecache has the capability to limit the number of writeback jobs
in progress. However, this feature was off by default. As such there
were some out-of-memory crashes observed when lowering the low
watermark while the cache is full.

This commit enables writeback limit by default. It is set to 256MiB or
1/16 of total system memory, whichever is smaller.

Cc: stable@vger.kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
index c3e59d8..dfb55fe 100644 (file)
--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -22,7 +22,7 @@
 
 #define HIGH_WATERMARK                 50
 #define LOW_WATERMARK                  45
-#define MAX_WRITEBACK_JOBS             0
+#define MAX_WRITEBACK_JOBS             min(0x10000000 / PAGE_SIZE, totalram_pages() / 16)
 #define ENDIO_LATENCY                  16
 #define WRITEBACK_LATENCY              64
 #define AUTOCOMMIT_BLOCKS_SSD          65536