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From: Mel Gorman <mgorman@techsingularity.net>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Chuck Lever <chuck.lever@oracle.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
	Alexander Duyck <alexander.duyck@gmail.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Matthew Wilcox <willy@infradead.org>,
	Ilias Apalodimas <ilias.apalodimas@linaro.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux-Net <netdev@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>,
	Linux-NFS <linux-nfs@vger.kernel.org>,
	Mel Gorman <mgorman@techsingularity.net>
Subject: [PATCH 4/9] mm/page_alloc: optimize code layout for __alloc_pages_bulk
Date: Thu, 25 Mar 2021 11:42:23 +0000	[thread overview]
Message-ID: <20210325114228.27719-5-mgorman@techsingularity.net> (raw)
In-Reply-To: <20210325114228.27719-1-mgorman@techsingularity.net>

From: Jesper Dangaard Brouer <brouer@redhat.com>

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: Minor changes and rebasing]
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
 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 be1e33a4df39..1ec18121268b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5001,7 +5001,7 @@ int __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
 	unsigned int alloc_flags;
 	int nr_populated = 0;
 
-	if (WARN_ON_ONCE(nr_pages <= 0))
+	if (unlikely(nr_pages <= 0))
 		return 0;
 
 	/*
@@ -5048,7 +5048,7 @@ int __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 */
@@ -5066,7 +5066,7 @@ int __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;
-- 
2.26.2



  parent reply	other threads:[~2021-03-25 11:43 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-25 11:42 [PATCH 0/9 v6] Introduce a bulk order-0 page allocator with two in-tree users Mel Gorman
2021-03-25 11:42 ` [PATCH 1/9] mm/page_alloc: Rename alloced to allocated Mel Gorman
2021-03-25 11:59   ` Matthew Wilcox
2021-04-12 10:01   ` Vlastimil Babka
2021-03-25 11:42 ` [PATCH 2/9] mm/page_alloc: Add a bulk page allocator Mel Gorman
2021-03-25 12:05   ` Matthew Wilcox
2021-03-25 12:37     ` Mel Gorman
2021-04-12 10:21   ` Vlastimil Babka
2021-04-12 10:59     ` Mel Gorman
2021-04-12 11:19       ` Mel Gorman
2021-03-25 11:42 ` [PATCH 3/9] mm/page_alloc: Add an array-based interface to the " Mel Gorman
2021-04-12 10:36   ` Vlastimil Babka
2021-03-25 11:42 ` Mel Gorman [this message]
2021-03-25 12:12   ` [PATCH 4/9] mm/page_alloc: optimize code layout for __alloc_pages_bulk Matthew Wilcox
2021-03-25 12:40     ` Mel Gorman
2021-04-12 10:41   ` Vlastimil Babka
2021-03-25 11:42 ` [PATCH 5/9] mm/page_alloc: inline __rmqueue_pcplist Mel Gorman
2021-04-12 10:59   ` Vlastimil Babka
2021-03-25 11:42 ` [PATCH 6/9] SUNRPC: Set rq_page_end differently Mel Gorman
2021-03-25 11:42 ` [PATCH 7/9] SUNRPC: Refresh rq_pages using a bulk page allocator Mel Gorman
2021-03-25 11:42 ` [PATCH 8/9] net: page_pool: refactor dma_map into own function page_pool_dma_map Mel Gorman
2021-03-25 11:42 ` [PATCH 9/9] net: page_pool: use alloc_pages_bulk in refill code path Mel Gorman
2021-03-25 13:33   ` Alexander Lobakin
2021-03-25 12:50 ` [PATCH 0/9 v6] Introduce a bulk order-0 page allocator with two in-tree users Matthew Wilcox
2021-03-25 13:25   ` Mel Gorman
2021-03-25 14:06     ` Uladzislau Rezki
2021-03-25 14:09       ` Matthew Wilcox
2021-03-25 14:13         ` Uladzislau Rezki
2021-03-25 14:26       ` Mel Gorman
2021-03-25 14:46         ` Uladzislau Rezki

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