From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753946AbaIHMgA (ORCPT ); Mon, 8 Sep 2014 08:36:00 -0400 Received: from zene.cmpxchg.org ([85.214.230.12]:60290 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752946AbaIHMf7 (ORCPT ); Mon, 8 Sep 2014 08:35:59 -0400 From: Johannes Weiner To: Andrew Morton Cc: Mel Gorman , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [patch] mm: page_alloc: fix zone allocation fairness on UP Date: Mon, 8 Sep 2014 08:35:51 -0400 Message-Id: <1410179751-28115-1-git-send-email-hannes@cmpxchg.org> X-Mailer: git-send-email 2.0.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: 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") Signed-off-by: Johannes Weiner Cc: Mel Gorman Cc: Vlastimil Babka Cc: "3.12+" --- mm/page_alloc.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) 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