[patch 169/178] mm/page_alloc: optimize code layout for __alloc_pages_bulk

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



From: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxxxxxxxx: minor changes and rebasing]
Link: https://lkml.kernel.org/r/20210325114228.27719-5-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Alexander Lobakin <alobakin@xxxxx>
Acked-By: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Alexander Duyck <alexander.duyck@xxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Chuck Lever <chuck.lever@xxxxxxxxxx>
Cc: David Miller <davem@xxxxxxxxxxxxx>
Cc: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/page_alloc.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/mm/page_alloc.c~mm-page_alloc-optimize-code-layout-for-__alloc_pages_bulk
+++ a/mm/page_alloc.c
@@ -5042,7 +5042,7 @@ unsigned long __alloc_pages_bulk(gfp_t g
 	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 g
 	 * 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 g
 
 		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;
_




[Index of Archives]     [Linux ARM Kernel]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Bugtraq]     [Linux OMAP]     [Linux MIPS]     [eCos]     [Asterisk Internet PBX]     [Linux API]

  Powered by Linux