From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753636AbaIHL5Z (ORCPT ); Mon, 8 Sep 2014 07:57:25 -0400 Received: from cantor2.suse.de ([195.135.220.15]:54305 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753533AbaIHL5X (ORCPT ); Mon, 8 Sep 2014 07:57:23 -0400 Date: Mon, 8 Sep 2014 12:57:18 +0100 From: Mel Gorman To: Andrew Morton Cc: Leon Romanovsky , Vlastimil Babka , Johannes Weiner , Linux Kernel , Linux-MM , Linux-FSDevel Subject: [PATCH] mm: page_alloc: Fix setting of ZONE_FAIR_DEPLETED on UP v2 Message-ID: <20140908115718.GL17501@suse.de> References: <1404893588-21371-1-git-send-email-mgorman@suse.de> <1404893588-21371-7-git-send-email-mgorman@suse.de> <53E4EC53.1050904@suse.cz> <20140811121241.GD7970@suse.de> <53E8B83D.1070004@suse.cz> <20140902140116.GD29501@cmpxchg.org> <20140905101451.GF17501@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit 4ffeaf35 (mm: page_alloc: reduce cost of the fair zone allocation policy) arguably broke the fair zone allocation policy on UP with these hunks. a/mm/page_alloc.c b/mm/page_alloc.c @@ -1612,6 +1612,9 @@ again: } __mod_zone_page_state(zone, NR_ALLOC_BATCH, -(1 << order)); + if (zone_page_state(zone, NR_ALLOC_BATCH) == 0 && + !zone_is_fair_depleted(zone)) + zone_set_flag(zone, ZONE_FAIR_DEPLETED); __count_zone_vm_events(PGALLOC, zone, 1 << order); zone_statistics(preferred_zone, zone, gfp_flags); @@ -1966,8 +1985,10 @@ zonelist_scan: if (alloc_flags & ALLOC_FAIR) { if (!zone_local(preferred_zone, zone)) break; - if (zone_page_state(zone, NR_ALLOC_BATCH) <= 0) + if (zone_is_fair_depleted(zone)) { + nr_fair_skipped++; continue; + } } A <= check was replaced with a ==. On SMP it doesn't matter because negative values are returned as zero due to per-CPU drift which is not possible in the UP case. Vlastimil Babka correctly pointed out that this can wrap negative due to high-order allocations. However, Leon Romanovsky pointed out that a <= check on zone_page_state was never correct as zone_page_state returns unsigned long so the root cause of the breakage was the <= check in the first place. zone_page_state is an API hazard because of the difference in behaviour between SMP and UP is very surprising. There is a good reason to allow NR_ALLOC_BATCH to go negative -- when the counter is reset the negative value takes recent activity into account. This patch makes zone_page_state behave the same on SMP and UP as saving one branch on UP is not likely to make a measurable performance difference. Reported-by: Vlastimil Babka Reported-by: Leon Romanovsky Signed-off-by: Mel Gorman --- include/linux/vmstat.h | 2 -- 1 file changed, 2 deletions(-) diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h index 82e7db7..cece0f0 100644 --- a/include/linux/vmstat.h +++ b/include/linux/vmstat.h @@ -131,10 +131,8 @@ static inline unsigned long zone_page_state(struct zone *zone, enum zone_stat_item item) { long x = atomic_long_read(&zone->vm_stat[item]); -#ifdef CONFIG_SMP if (x < 0) x = 0; -#endif return x; } From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mel Gorman Subject: [PATCH] mm: page_alloc: Fix setting of ZONE_FAIR_DEPLETED on UP v2 Date: Mon, 8 Sep 2014 12:57:18 +0100 Message-ID: <20140908115718.GL17501@suse.de> References: <1404893588-21371-1-git-send-email-mgorman@suse.de> <1404893588-21371-7-git-send-email-mgorman@suse.de> <53E4EC53.1050904@suse.cz> <20140811121241.GD7970@suse.de> <53E8B83D.1070004@suse.cz> <20140902140116.GD29501@cmpxchg.org> <20140905101451.GF17501@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Cc: Leon Romanovsky , Vlastimil Babka , Johannes Weiner , Linux Kernel , Linux-MM , Linux-FSDevel To: Andrew Morton Return-path: Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org Commit 4ffeaf35 (mm: page_alloc: reduce cost of the fair zone allocation policy) arguably broke the fair zone allocation policy on UP with these hunks. a/mm/page_alloc.c b/mm/page_alloc.c @@ -1612,6 +1612,9 @@ again: } __mod_zone_page_state(zone, NR_ALLOC_BATCH, -(1 << order)); + if (zone_page_state(zone, NR_ALLOC_BATCH) == 0 && + !zone_is_fair_depleted(zone)) + zone_set_flag(zone, ZONE_FAIR_DEPLETED); __count_zone_vm_events(PGALLOC, zone, 1 << order); zone_statistics(preferred_zone, zone, gfp_flags); @@ -1966,8 +1985,10 @@ zonelist_scan: if (alloc_flags & ALLOC_FAIR) { if (!zone_local(preferred_zone, zone)) break; - if (zone_page_state(zone, NR_ALLOC_BATCH) <= 0) + if (zone_is_fair_depleted(zone)) { + nr_fair_skipped++; continue; + } } A <= check was replaced with a ==. On SMP it doesn't matter because negative values are returned as zero due to per-CPU drift which is not possible in the UP case. Vlastimil Babka correctly pointed out that this can wrap negative due to high-order allocations. However, Leon Romanovsky pointed out that a <= check on zone_page_state was never correct as zone_page_state returns unsigned long so the root cause of the breakage was the <= check in the first place. zone_page_state is an API hazard because of the difference in behaviour between SMP and UP is very surprising. There is a good reason to allow NR_ALLOC_BATCH to go negative -- when the counter is reset the negative value takes recent activity into account. This patch makes zone_page_state behave the same on SMP and UP as saving one branch on UP is not likely to make a measurable performance difference. Reported-by: Vlastimil Babka Reported-by: Leon Romanovsky Signed-off-by: Mel Gorman --- include/linux/vmstat.h | 2 -- 1 file changed, 2 deletions(-) diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h index 82e7db7..cece0f0 100644 --- a/include/linux/vmstat.h +++ b/include/linux/vmstat.h @@ -131,10 +131,8 @@ static inline unsigned long zone_page_state(struct zone *zone, enum zone_stat_item item) { long x = atomic_long_read(&zone->vm_stat[item]); -#ifdef CONFIG_SMP if (x < 0) x = 0; -#endif return x; } -- 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/ . Don't email: email@kvack.org