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| author | Minchan Kim <minchan.kim@gmail.com> | 2011-01-13 15:46:27 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-01-13 17:32:38 -0800 |
| commit | 240c879f20a605346705be24253bc9fc6fa8a106 (patch) | |
| tree | 85c38509483aa5f69d3dea5daa21412dd2e6aced /mm/page-writeback.c | |
| parent | ecb256f815232b35ae8382cff36ca8ce0bbd077e (diff) | |
| download | lwn-240c879f20a605346705be24253bc9fc6fa8a106.tar.gz lwn-240c879f20a605346705be24253bc9fc6fa8a106.zip | |
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/page-writeback.c')
| -rw-r--r-- | mm/page-writeback.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 28763b8bdbdd..2cb01f6ec5d0 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 |