tree 85c38509483aa5f69d3dea5daa21412dd2e6aced
parent ecb256f815232b35ae8382cff36ca8ce0bbd077e
author Minchan Kim <minchan.kim@gmail.com> 1294962387 -0800
committer Linus Torvalds <torvalds@linux-foundation.org> 1294968758 -0800

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>