From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754266AbcIZQUh (ORCPT ); Mon, 26 Sep 2016 12:20:37 -0400 Received: from mx2.suse.de ([195.135.220.15]:48870 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753556AbcIZQUe (ORCPT ); Mon, 26 Sep 2016 12:20:34 -0400 From: Vlastimil Babka To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Linus Torvalds , Arkadiusz Miskiewicz , Ralf-Peter Rohbeck , Olaf Hering , Vlastimil Babka , Michal Hocko , Mel Gorman , Joonsoo Kim , David Rientjes , Rik van Riel , Hillf Danton , Michal Hocko Subject: [PATCH 4/4] mm, compaction: restrict fragindex to costly orders Date: Mon, 26 Sep 2016 18:20:25 +0200 Message-Id: <20160926162025.21555-5-vbabka@suse.cz> X-Mailer: git-send-email 2.10.0 In-Reply-To: <20160926162025.21555-1-vbabka@suse.cz> References: <20160926162025.21555-1-vbabka@suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Fragmentation index and the vm.extfrag_threshold sysctl is meant as a heuristic to prevent excessive compaction for costly orders (i.e. THP). It's unlikely to make any difference for non-costly orders, especially with the default threshold. But we cannot afford any uncertainty for the non-costly orders where the only alternative to successful reclaim/compaction is OOM. After the recent patches we are guaranteed maximum effort without heuristics from compaction before deciding OOM, and fragindex is the last remaining heuristic. Therefore skip fragindex altogether for non-costly orders. Suggested-by: Michal Hocko Signed-off-by: Vlastimil Babka Cc: Michal Hocko Cc: Mel Gorman Cc: Joonsoo Kim Cc: David Rientjes Cc: Rik van Riel --- mm/compaction.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 5ff7f801c345..badb92bf14b4 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1435,9 +1435,14 @@ enum compact_result compaction_suitable(struct zone *zone, int order, * index towards 0 implies failure is due to lack of memory * index towards 1000 implies failure is due to fragmentation * - * Only compact if a failure would be due to fragmentation. + * Only compact if a failure would be due to fragmentation. Also + * ignore fragindex for non-costly orders where the alternative to + * a successful reclaim/compaction is OOM. Fragindex and the + * vm.extfrag_threshold sysctl is meant as a heuristic to prevent + * excessive compaction for costly orders, but it should not be at the + * expense of system stability. */ - if (ret == COMPACT_CONTINUE) { + if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) { fragindex = fragmentation_index(zone, order); if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold) return COMPACT_NOT_SUITABLE_ZONE; -- 2.10.0