dm writecache: set a default MAX_WRITEBACK_JOBS

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>

diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
index d74c5a7a0ab496f5a1154548de8cacc64e5ecc6b..d572135cd43fa7136ebce00e20bb548c4ce80c58 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