Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755927Ab1EQQXE (ORCPT ); Tue, 17 May 2011 12:23:04 -0400 Received: from cantor2.suse.de ([195.135.220.15]:53540 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755715Ab1EQQXC (ORCPT ); Tue, 17 May 2011 12:23:02 -0400 Date: Tue, 17 May 2011 17:22:56 +0100 From: Mel Gorman To: Christoph Lameter Cc: David Rientjes , Andrew Morton , James Bottomley , Colin King , Raghavendra D Prabhu , Jan Kara , Chris Mason , Pekka Enberg , Rik van Riel , Johannes Weiner , linux-fsdevel , linux-mm , linux-kernel , linux-ext4 Subject: Re: [PATCH 3/4] mm: slub: Do not take expensive steps for SLUBs speculative high-order allocations Message-ID: <20110517162256.GO5279@suse.de> References: <1305295404-12129-1-git-send-email-mgorman@suse.de> <1305295404-12129-4-git-send-email-mgorman@suse.de> <20110517084227.GI5279@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 Content-Length: 1953 Lines: 42 On Tue, May 17, 2011 at 08:51:47AM -0500, Christoph Lameter wrote: > On Tue, 17 May 2011, Mel Gorman wrote: > > > entirely. Christoph wants to maintain historic behaviour of SLUB to > > maximise the number of high-order pages it uses and at the end of the > > day, which option performs better depends entirely on the workload > > and machine configuration. > > That is not what I meant. I would like more higher order allocations to > succeed. That does not mean that slubs allocation methods and flags passed > have to stay the same. You can change the slub behavior if it helps. > In this particular patch, the success rate for high order allocations would likely decrease in low memory conditions albeit the latency when calling the page allocator will be lower and the disruption to the system will be less (no copying or reclaim of pages). My expectation would be that it's cheaper for SLUB to fall back than compact memory or reclaim pages even if this means a slab page is smaller until more memory is free. However, if the "goodness" criteria is high order allocation success rate, the patch shouldn't be merged. > I am just suspicious of compaction. If these mods are needed to reduce the > amount of higher order pages then compaction does not have the > beneficial effect that it should have. It does not actually > increase the available higher order pages. Fix that first. > The problem being addressed was the machine being hung at worst and in other cases having kswapd pinned at 99-100% CPU. It's now been shown that modifying SLUB is not necessary to fix this because the bug was in page reclaim. The high-order allocation success rate didn't come into it. -- Mel Gorman SUSE Labs -- 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/