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@xxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
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))
--
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