Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754291AbbGWU60 (ORCPT ); Thu, 23 Jul 2015 16:58:26 -0400 Received: from mail-pa0-f44.google.com ([209.85.220.44]:35575 "EHLO mail-pa0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753635AbbGWU6W (ORCPT ); Thu, 23 Jul 2015 16:58:22 -0400 Date: Thu, 23 Jul 2015 13:58:20 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Joonsoo Kim cc: Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Hugh Dickins , Andrea Arcangeli , "Kirill A. Shutemov" , Rik van Riel , Mel Gorman Subject: Re: [RFC 1/4] mm, compaction: introduce kcompactd In-Reply-To: <20150723060348.GF4449@js1304-P5Q-DELUXE> Message-ID: References: <1435826795-13777-1-git-send-email-vbabka@suse.cz> <1435826795-13777-2-git-send-email-vbabka@suse.cz> <20150723060348.GF4449@js1304-P5Q-DELUXE> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1936 Lines: 37 On Thu, 23 Jul 2015, Joonsoo Kim wrote: > > The slub allocator does try to allocate its high-order memory with > > __GFP_WAIT before falling back to lower orders if possible. I would think > > that this would be the greatest sign of on-demand memory compaction being > > a problem, especially since CONFIG_SLUB is the default, but I haven't seen > > such reports. > > In fact, some of our product had trouble with slub's high order > allocation 5 months ago. At that time, compaction didn't make high order > page and compaction attempts are frequently deferred. It also causes many > reclaim to make high order page so I suggested masking out __GFP_WAIT > and adding __GFP_NO_KSWAPD when trying slub's high order allocation to > reduce reclaim/compaction overhead. Although using high order page in slub > has some gains that reducing internal fragmentation and reducing management > overhead, benefit is marginal compared to the cost at making high order > page. This solution improves system response time for our case. I planned > to submit the patch but it is delayed due to my laziness. :) > Hi Joonsoo, On a fragmented machine I can certainly understand that the overhead involved in allocating the high-order page outweighs the benefit later and it's better to fallback more quickly to page orders if the cache allows it. I believe that this would be improved by the suggestion of doing background synchronous compaction. So regardless of whether __GFP_WAIT is set, if the allocation fails then we can kick off background compaction that will hopefully defragment memory for future callers. That should make high-order atomic allocations more successful as well. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/