diff options
| author | Mateusz Nosek <mateusznosek0@gmail.com> | 2020-04-01 21:09:47 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-04-02 09:35:30 -0700 |
| commit | 736838e964c3282a3472626a97f9f49e020185e0 (patch) | |
| tree | 91d8ee8f884a79eedce282cc485248090d13ee5f /mm/page_alloc.c | |
| parent | ee8eb9a5fe86332c6c6163a2322376f960026596 (diff) | |
mm, pagealloc: micro-optimisation: save two branches on hot page allocation path
This patch makes ALLOC_KSWAPD equal to __GFP_KSWAPD_RECLAIM (cast to int).
Thanks to that code like:
if (gfp_mask & __GFP_KSWAPD_RECLAIM)
alloc_flags |= ALLOC_KSWAPD;
can be changed to:
alloc_flags |= (__force int) (gfp_mask &__GFP_KSWAPD_RECLAIM);
Thanks to this one branch less is generated in the assembly.
In case of ALLOC_KSWAPD flag two branches are saved, first one in code
that always executes in the beginning of page allocation and the second
one in loop in page allocator slowpath.
Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Link: http://lkml.kernel.org/r/20200304162118.14784-1-mateusznosek0@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/page_alloc.c')
| -rw-r--r-- | mm/page_alloc.c | 22 |
1 files changed, 14 insertions, 8 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index fb0b3ff17571..2dedf5a1e49c 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3536,10 +3536,13 @@ static bool zone_allows_reclaim(struct zone *local_zone, struct zone *zone) static inline unsigned int alloc_flags_nofragment(struct zone *zone, gfp_t gfp_mask) { - unsigned int alloc_flags = 0; + unsigned int alloc_flags; - if (gfp_mask & __GFP_KSWAPD_RECLAIM) - alloc_flags |= ALLOC_KSWAPD; + /* + * __GFP_KSWAPD_RECLAIM is assumed to be the same as ALLOC_KSWAPD + * to save a branch. + */ + alloc_flags = (__force int) (gfp_mask & __GFP_KSWAPD_RECLAIM); #ifdef CONFIG_ZONE_DMA32 if (!zone) @@ -4175,8 +4178,13 @@ gfp_to_alloc_flags(gfp_t gfp_mask) { unsigned int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET; - /* __GFP_HIGH is assumed to be the same as ALLOC_HIGH to save a branch. */ + /* + * __GFP_HIGH is assumed to be the same as ALLOC_HIGH + * and __GFP_KSWAPD_RECLAIM is assumed to be the same as ALLOC_KSWAPD + * to save two branches. + */ BUILD_BUG_ON(__GFP_HIGH != (__force gfp_t) ALLOC_HIGH); + BUILD_BUG_ON(__GFP_KSWAPD_RECLAIM != (__force gfp_t) ALLOC_KSWAPD); /* * The caller may dip into page reserves a bit more if the caller @@ -4184,7 +4192,8 @@ gfp_to_alloc_flags(gfp_t gfp_mask) * policy or is asking for __GFP_HIGH memory. GFP_ATOMIC requests will * set both ALLOC_HARDER (__GFP_ATOMIC) and ALLOC_HIGH (__GFP_HIGH). */ - alloc_flags |= (__force int) (gfp_mask & __GFP_HIGH); + alloc_flags |= (__force int) + (gfp_mask & (__GFP_HIGH | __GFP_KSWAPD_RECLAIM)); if (gfp_mask & __GFP_ATOMIC) { /* @@ -4201,9 +4210,6 @@ gfp_to_alloc_flags(gfp_t gfp_mask) } else if (unlikely(rt_task(current)) && !in_interrupt()) alloc_flags |= ALLOC_HARDER; - if (gfp_mask & __GFP_KSWAPD_RECLAIM) - alloc_flags |= ALLOC_KSWAPD; - #ifdef CONFIG_CMA if (gfpflags_to_migratetype(gfp_mask) == MIGRATE_MOVABLE) alloc_flags |= ALLOC_CMA; |