[PATCH] writeback: skip balance_dirty_pages() for in-memory fs

Wu Fengguang
2010-12-17T11:21:18Z

This avoids unnecessary checks and dirty throttling on tmpfs/ramfs.

It also prevents

[ 388.126563] BUG: unable to handle kernel NULL pointer dereference at 0000000000000050

in the balance_dirty_pages tracepoint, which will call

dev_name(mapping->backing_dev_info->dev)

but shmem_backing_dev_info.dev is NULL.

CC: Hugh Dickins <hughd@google.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
mm/page-writeback.c | 3 +++
1 file changed, 3 insertions(+)

--- linux-next.orig/mm/page-writeback.c 2010-12-17 19:09:19.000000000 +0800
+++ linux-next/mm/page-writeback.c 2010-12-17 19:09:22.000000000 +0800
@@ -899,6 +899,9 @@ void balance_dirty_pages_ratelimited_nr(
{
struct backing_dev_info *bdi = mapping->backing_dev_info;

+ if (!bdi_cap_account_dirty(bdi))
+ return;
+
current->nr_dirtied += nr_pages_dirtied;

if (unlikely(!current->nr_dirtied_pause))