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Subject[PATCH 10/22] Remove a branch by assuming __GFP_HIGH == ALLOC_HIGH
Date
Allocations that specify __GFP_HIGH get the ALLOC_HIGH flag. If these
flags are equal to each other, we can eliminate a branch.

[akpm@linux-foundation.org: Suggested the hack]
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Pekka Enberg <penberg@cs.helsinki.fi>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
mm/page_alloc.c | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0d23795..4f9cdaa 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1619,14 +1619,16 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET;
const gfp_t wait = gfp_mask & __GFP_WAIT;

+ /* __GFP_HIGH is assumed to be the same as ALLOC_HIGH to save a branch. */
+ BUILD_BUG_ON(__GFP_HIGH != ALLOC_HIGH);
+
/*
* The caller may dip into page reserves a bit more if the caller
* cannot run direct reclaim, or if the caller has realtime scheduling
* policy or is asking for __GFP_HIGH memory. GFP_ATOMIC requests will
* set both ALLOC_HARDER (!wait) and ALLOC_HIGH (__GFP_HIGH).
*/
- if (gfp_mask & __GFP_HIGH)
- alloc_flags |= ALLOC_HIGH;
+ alloc_flags |= (gfp_mask & __GFP_HIGH);

if (!wait) {
alloc_flags |= ALLOC_HARDER;
--
1.5.6.5


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