From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f171.google.com (mail-we0-f171.google.com [74.125.82.171]) by kanga.kvack.org (Postfix) with ESMTP id CD62D6B0038 for ; Tue, 9 Sep 2014 09:15:49 -0400 (EDT) Received: by mail-we0-f171.google.com with SMTP id p10so679009wes.2 for ; Tue, 09 Sep 2014 06:15:49 -0700 (PDT) Received: from gum.cmpxchg.org (gum.cmpxchg.org. [85.214.110.215]) by mx.google.com with ESMTPS id bl1si17094990wjb.144.2014.09.09.06.15.48 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 09 Sep 2014 06:15:48 -0700 (PDT) Date: Tue, 9 Sep 2014 09:15:40 -0400 From: Johannes Weiner Subject: [patch resend] mm: page_alloc: fix zone allocation fairness on UP Message-ID: <20140909131540.GA10568@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: Mel Gorman , Vlastimil Babka , Leon Romanovsky , linux-mm@kvack.org, linux-kernel@vger.kernel.org The zone allocation batches can easily underflow due to higher-order allocations or spills to remote nodes. On SMP that's fine, because underflows are expected from concurrency and dealt with by returning 0. But on UP, zone_page_state will just return a wrapped unsigned long, which will get past the <= 0 check and then consider the zone eligible until its watermarks are hit. 3a025760fc15 ("mm: page_alloc: spill to remote nodes before waking kswapd") already made the counter-resetting use atomic_long_read() to accomodate underflows from remote spills, but it didn't go all the way with it. Make it clear that these batches are expected to go negative regardless of concurrency, and use atomic_long_read() everywhere. Fixes: 81c0a2bb515f ("mm: page_alloc: fair zone allocator policy") Reported-by: Vlastimil Babka Reported-by: Leon Romanovsky Signed-off-by: Johannes Weiner Acked-by: Mel Gorman Cc: "3.12+" --- mm/page_alloc.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) Sorry I forgot to CC you, Leon. Resend with updated Tags. diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 18cee0d4c8a2..eee961958021 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1612,7 +1612,7 @@ again: } __mod_zone_page_state(zone, NR_ALLOC_BATCH, -(1 << order)); - if (zone_page_state(zone, NR_ALLOC_BATCH) == 0 && + if (atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH]) <= 0 && !zone_is_fair_depleted(zone)) zone_set_flag(zone, ZONE_FAIR_DEPLETED); @@ -5701,9 +5701,8 @@ static void __setup_per_zone_wmarks(void) zone->watermark[WMARK_HIGH] = min_wmark_pages(zone) + (tmp >> 1); __mod_zone_page_state(zone, NR_ALLOC_BATCH, - high_wmark_pages(zone) - - low_wmark_pages(zone) - - zone_page_state(zone, NR_ALLOC_BATCH)); + high_wmark_pages(zone) - low_wmark_pages(zone) - + atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH])); setup_zone_migrate_reserve(zone); spin_unlock_irqrestore(&zone->lock, flags); -- 2.0.4 -- 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/ . Don't email: email@kvack.org