linux-kernel - [PATCH 15/28] mm, page_alloc: Move might_sleep

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Message-Id: <1460711275-1130-3-git-send-email-mgorman@techsingularity.net>
Date:	Fri, 15 Apr 2016 10:07:42 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Vlastimil Babka <vbabka@...e.cz>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 15/28] mm, page_alloc: Move might_sleep_if check to the allocator slowpath

There is a debugging check for callers that specify __GFP_DIRECT_RECLAIM
from a context that cannot sleep. Triggering this is almost certainly
a bug but it's also overhead in the fast path. Move the check to the slow
path. It'll be harder to trigger as it'll only be checked when watermarks
are depleted but it'll also only be checked in a path that can sleep.

Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 mm/page_alloc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 21aaef6ddd7a..9ef2f4ab9ca5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3176,6 +3176,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 		return NULL;
 	}
 
+	might_sleep_if(gfp_mask & __GFP_DIRECT_RECLAIM);
+
 	/*
 	 * We also sanity check to catch abuse of atomic reserves being used by
 	 * callers that are not in atomic context.
@@ -3369,8 +3371,6 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
 
 	lockdep_trace_alloc(gfp_mask);
 
-	might_sleep_if(gfp_mask & __GFP_DIRECT_RECLAIM);
-
 	if (should_fail_alloc_page(gfp_mask, order))
 		return NULL;
 
-- 
2.6.4