From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752450Ab1BIPq1 (ORCPT ); Wed, 9 Feb 2011 10:46:27 -0500 Received: from zene.cmpxchg.org ([85.214.230.12]:38531 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751921Ab1BIPq0 (ORCPT ); Wed, 9 Feb 2011 10:46:26 -0500 Date: Wed, 9 Feb 2011 16:46:06 +0100 From: Johannes Weiner To: Andrew Morton Cc: Andrea Arcangeli , Mel Gorman , Rik van Riel , Michal Hocko , Kent Overstreet , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [patch] vmscan: fix zone shrinking exit when scan work is done Message-ID: <20110209154606.GJ27110@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, I think this should fix the problem of processes getting stuck in reclaim that has been reported several times. Kent actually single-stepped through this code and noted that it was never exiting shrink_zone(), which really narrowed it down a lot, considering the tons of nested loops from the allocator down to the list shrinking. Hannes --- From: Johannes Weiner Subject: vmscan: fix zone shrinking exit when scan work is done '3e7d344 mm: vmscan: reclaim order-0 and use compaction instead of lumpy reclaim' introduced an indefinite loop in shrink_zone(). It meant to break out of this loop when no pages had been reclaimed and not a single page was even scanned. The way it would detect the latter is by taking a snapshot of sc->nr_scanned at the beginning of the function and comparing it against the new sc->nr_scanned after the scan loop. But it would re-iterate without updating that snapshot, looping forever if sc->nr_scanned changed at least once since shrink_zone() was invoked. This is not the sole condition that would exit that loop, but it requires other processes to change the zone state, as the reclaimer that is stuck obviously can not anymore. This is only happening for higher-order allocations, where reclaim is run back to back with compaction. Reported-by: Michal Hocko Reported-by: Kent Overstreet Signed-off-by: Johannes Weiner --- mm/vmscan.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 148c6e6..17497d0 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1882,12 +1882,12 @@ static void shrink_zone(int priority, struct zone *zone, unsigned long nr[NR_LRU_LISTS]; unsigned long nr_to_scan; enum lru_list l; - unsigned long nr_reclaimed; + unsigned long nr_reclaimed, nr_scanned; unsigned long nr_to_reclaim = sc->nr_to_reclaim; - unsigned long nr_scanned = sc->nr_scanned; restart: nr_reclaimed = 0; + nr_scanned = sc->nr_scanned; get_scan_count(zone, sc, nr, priority); while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] || -- 1.7.4 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id 8DFCE8D0039 for ; Wed, 9 Feb 2011 10:46:25 -0500 (EST) Date: Wed, 9 Feb 2011 16:46:06 +0100 From: Johannes Weiner Subject: [patch] vmscan: fix zone shrinking exit when scan work is done Message-ID: <20110209154606.GJ27110@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Andrea Arcangeli , Mel Gorman , Rik van Riel , Michal Hocko , Kent Overstreet , linux-mm@kvack.org, linux-kernel@vger.kernel.org Hi, I think this should fix the problem of processes getting stuck in reclaim that has been reported several times. Kent actually single-stepped through this code and noted that it was never exiting shrink_zone(), which really narrowed it down a lot, considering the tons of nested loops from the allocator down to the list shrinking. Hannes --- From: Johannes Weiner Subject: vmscan: fix zone shrinking exit when scan work is done '3e7d344 mm: vmscan: reclaim order-0 and use compaction instead of lumpy reclaim' introduced an indefinite loop in shrink_zone(). It meant to break out of this loop when no pages had been reclaimed and not a single page was even scanned. The way it would detect the latter is by taking a snapshot of sc->nr_scanned at the beginning of the function and comparing it against the new sc->nr_scanned after the scan loop. But it would re-iterate without updating that snapshot, looping forever if sc->nr_scanned changed at least once since shrink_zone() was invoked. This is not the sole condition that would exit that loop, but it requires other processes to change the zone state, as the reclaimer that is stuck obviously can not anymore. This is only happening for higher-order allocations, where reclaim is run back to back with compaction. Reported-by: Michal Hocko Reported-by: Kent Overstreet Signed-off-by: Johannes Weiner --- mm/vmscan.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 148c6e6..17497d0 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1882,12 +1882,12 @@ static void shrink_zone(int priority, struct zone *zone, unsigned long nr[NR_LRU_LISTS]; unsigned long nr_to_scan; enum lru_list l; - unsigned long nr_reclaimed; + unsigned long nr_reclaimed, nr_scanned; unsigned long nr_to_reclaim = sc->nr_to_reclaim; - unsigned long nr_scanned = sc->nr_scanned; restart: nr_reclaimed = 0; + nr_scanned = sc->nr_scanned; get_scan_count(zone, sc, nr, priority); while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] || -- 1.7.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . 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