From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755945Ab0IJC5F (ORCPT ); Thu, 9 Sep 2010 22:57:05 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:38245 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753465Ab0IJC5C (ORCPT ); Thu, 9 Sep 2010 22:57:02 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: Mel Gorman Subject: Re: [PATCH 3/3] mm: page allocator: Drain per-cpu lists after direct reclaim allocation fails Cc: kosaki.motohiro@jp.fujitsu.com, Christoph Lameter , Andrew Morton , Linux Kernel List , linux-mm@kvack.org, Rik van Riel , Johannes Weiner , Minchan Kim , KAMEZAWA Hiroyuki In-Reply-To: <20100909150558.GB340@csn.ul.ie> References: <20100909150558.GB340@csn.ul.ie> Message-Id: <20100910115503.C95E.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Fri, 10 Sep 2010 11:56:59 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Thu, Sep 09, 2010 at 09:32:52AM -0500, Christoph Lameter wrote: > > On Thu, 9 Sep 2010, Mel Gorman wrote: > > > > > > This will have the effect of never sending IPIs for slab allocations since > > > > they do not do allocations for orders > PAGE_ALLOC_COSTLY_ORDER. > > > > > > > > > > The question is how severe is that? There is somewhat of an expectation > > > that the lower orders free naturally so it the IPI justified? That said, > > > our historical behaviour would have looked like > > > > > > if (!page && !drained && order) { > > > drain_all_pages(); > > > draiained = true; > > > goto retry; > > > } > > > > > > Play it safe for now and go with that? > > > > I am fine with no IPIs for order <= COSTLY. Just be aware that this is > > a change that may have some side effects. > > I made the choice consciously. I felt that if slab or slub were depending on > IPIs to make successful allocations in low-memory conditions that it would > experience varying stalls on bigger machines due to increased interrupts that > might be difficult to diagnose while not necessarily improving allocation > success rates. I also considered that if the machine is under pressure then > slab and slub may also be releasing pages of the same order and effectively > recycling their pages without depending on IPIs. +1. In these days, average numbers of CPUs are increasing. So we need to be afraid IPI storm than past.