linux-kernel - [RFC 02/13] mm, page_alloc: set alloc

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Message-Id: <1462865763-22084-3-git-send-email-vbabka@suse.cz>
Date:	Tue, 10 May 2016 09:35:52 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Johannes Weiner <hannes@...xchg.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: [RFC 02/13] mm, page_alloc: set alloc_flags only once in slowpath

In __alloc_pages_slowpath(), alloc_flags doesn't change after it's initialized,
so move the initialization above the retry: label. Also make the comment above
the initialization more descriptive.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/page_alloc.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a50184ec6ca0..91fbf6f95403 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3579,17 +3579,17 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 				(__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)))
 		gfp_mask &= ~__GFP_ATOMIC;
 
-retry:
-	if (gfp_mask & __GFP_KSWAPD_RECLAIM)
-		wake_all_kswapds(order, ac);
-
 	/*
-	 * OK, we're below the kswapd watermark and have kicked background
-	 * reclaim. Now things get more complex, so set up alloc_flags according
-	 * to how we want to proceed.
+	 * The fast path uses conservative alloc_flags to succeed only until
+	 * kswapd needs to be woken up, and to avoid the cost of setting up
+	 * alloc_flags precisely. So we do that now.
 	 */
 	alloc_flags = gfp_to_alloc_flags(gfp_mask);
 
+retry:
+	if (gfp_mask & __GFP_KSWAPD_RECLAIM)
+		wake_all_kswapds(order, ac);
+
 	/* This is the last chance, in general, before the goto nopage. */
 	page = get_page_from_freelist(gfp_mask, order,
 				alloc_flags & ~ALLOC_NO_WATERMARKS, ac);
-- 
2.8.2