linux-kernel - [PATCH 2/2] mm, vmscan: wake up all pfmemalloc-throttled processes at once

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Date:	Fri, 19 Dec 2014 14:01:56 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Rik van Riel <riel@...hat.com>, <stable@...r.kernel.org>
Subject: [PATCH 2/2] mm, vmscan: wake up all pfmemalloc-throttled processes at once

Kswapd in balance_pgdate() currently uses wake_up() on processes waiting in
throttle_direct_reclaim(), which only wakes up a single process. This might
leave processes waiting for longer than necessary, until the check is reached
in the next loop iteration. Processes might also be left waiting if zone was
fully balanced in single iteration. Note that the comment in balance_pgdat()
also says "Wake them", so waking up a single process does not seem intentional.

Thus, replace wake_up() with wake_up_all().

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Michal Hocko <mhocko@...e.cz>
Cc: Vladimir Davydov <vdavydov@...allels.com>
Cc: Rik van Riel <riel@...hat.com>
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 162c3f8..60b999c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3178,7 +3178,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 		 */
 		if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
 				pfmemalloc_watermark_ok(pgdat))
-			wake_up(&pgdat->pfmemalloc_wait);
+			wake_up_all(&pgdat->pfmemalloc_wait);
 
 		/*
 		 * Fragmentation may mean that the system cannot be rebalanced
-- 
2.1.2

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