From ce76f9a1d9a21c2633dcd2a5605f923286e16e1d Mon Sep 17 00:00:00 2001
From: Jesper Dangaard Brouer <brouer@redhat.com>
Date: Thu, 29 Apr 2021 23:01:51 -0700
Subject: [PATCH] mm/page_alloc: optimize code layout for __alloc_pages_bulk
Looking at perf-report and ASM-code for __alloc_pages_bulk() it is clear
that the code activated is suboptimal. The compiler guesses wrong and
places unlikely code at the beginning. Due to the use of WARN_ON_ONCE()
macro the UD2 asm instruction is added to the code, which confuse the
I-cache prefetcher in the CPU.
[mgorman@techsingularity.net: minor changes and rebasing]
Link: https://lkml.kernel.org/r/20210325114228.27719-5-mgorman@techsingularity.net
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Alexander Lobakin <alobakin@pm.me>
Acked-By: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: David Miller <davem@davemloft.net>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
mm/page_alloc.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e240704b5d399..3f2291695b19e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5042,7 +5042,7 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
unsigned int alloc_flags = ALLOC_WMARK_LOW;
int nr_populated = 0;
- if (WARN_ON_ONCE(nr_pages <= 0))
+ if (unlikely(nr_pages <= 0))
return 0;
/*
@@ -5089,7 +5089,7 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
* If there are no allowed local zones that meets the watermarks then
* try to allocate a single page and reclaim if necessary.
*/
- if (!zone)
+ if (unlikely(!zone))
goto failed;
/* Attempt the batch allocation */
@@ -5107,7 +5107,7 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
page = __rmqueue_pcplist(zone, ac.migratetype, alloc_flags,
pcp, pcp_list);
- if (!page) {
+ if (unlikely(!page)) {
/* Try and get at least one page */
if (!nr_populated)
goto failed_irq;
--
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