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authorMinchan Kim <minchan.kim@gmail.com>2011-01-13 15:46:27 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2011-01-13 17:32:38 -0800
commit240c879f20a605346705be24253bc9fc6fa8a106 (patch)
tree85c38509483aa5f69d3dea5daa21412dd2e6aced /mm
parentecb256f815232b35ae8382cff36ca8ce0bbd077e (diff)
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writeback: avoid unnecessary determine_dirtyable_memory call
I think determine_dirtyable_memory() is a rather costly function since it need many atomic reads for gathering zone/global page state. But when we use vm_dirty_bytes && dirty_background_bytes, we don't need that costly calculation. This patch eliminates such unnecessary overhead. NOTE : newly added if condition might add overhead in normal path. But it should be _really_ small because anyway we need the access both vm_dirty_bytes and dirty_background_bytes so it is likely to hit the cache. [akpm@linux-foundation.org: fix used-uninitialised warning] Signed-off-by: Minchan Kim <minchan.kim@gmail.com> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/page-writeback.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 28763b8bdbd..2cb01f6ec5d 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -410,9 +410,12 @@ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
{
unsigned long background;
unsigned long dirty;
- unsigned long available_memory = determine_dirtyable_memory();
+ unsigned long uninitialized_var(available_memory);
struct task_struct *tsk;
+ if (!vm_dirty_bytes || !dirty_background_bytes)
+ available_memory = determine_dirtyable_memory();
+
if (vm_dirty_bytes)
dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
else