[dm-devel] [PATCH] dm-writecache: set MAX_WRITEBACK_JOBS

[Mikulas Patocka]

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

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

Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>

---
 drivers/md/dm-writecache.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/drivers/md/dm-writecache.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-writecache.c	2022-07-13 13:07:52.000000000 +0200
+++ linux-2.6/drivers/md/dm-writecache.c	2022-07-13 13:08:19.000000000 +0200
@@ -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