From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754460Ab0BVUfI (ORCPT ); Mon, 22 Feb 2010 15:35:08 -0500 Received: from mx1.redhat.com ([209.132.183.28]:16037 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753135Ab0BVUfF (ORCPT ); Mon, 22 Feb 2010 15:35:05 -0500 Message-ID: <4B82EA4D.8040305@redhat.com> Date: Mon, 22 Feb 2010 15:34:21 -0500 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.5) Gecko/20091209 Fedora/3.0-4.fc12 Lightning/1.0pre Thunderbird/3.0 MIME-Version: 1.0 To: Johannes Weiner CC: Andrew Morton , KOSAKI Motohiro , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [patch 3/3] vmscan: detect mapped file pages used only once References: <1266868150-25984-1-git-send-email-hannes@cmpxchg.org> <1266868150-25984-4-git-send-email-hannes@cmpxchg.org> In-Reply-To: <1266868150-25984-4-git-send-email-hannes@cmpxchg.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/22/2010 02:49 PM, Johannes Weiner wrote: > The VM currently assumes that an inactive, mapped and referenced file > page is in use and promotes it to the active list. > > However, every mapped file page starts out like this and thus a problem > arises when workloads create a stream of such pages that are used only > for a short time. By flooding the active list with those pages, the VM > quickly gets into trouble finding eligible reclaim canditates. The > result is long allocation latencies and eviction of the wrong pages. > > This patch reuses the PG_referenced page flag (used for unmapped file > pages) to implement a usage detection that scales with the speed of > LRU list cycling (i.e. memory pressure). > > If the scanner encounters those pages, the flag is set and the page > cycled again on the inactive list. Only if it returns with another > page table reference it is activated. Otherwise it is reclaimed as > 'not recently used cache'. > > This effectively changes the minimum lifetime of a used-once mapped > file page from a full memory cycle to an inactive list cycle, which > allows it to occur in linear streams without affecting the stable > working set of the system. > > Signed-off-by: Johannes Weiner Reviewed-by: Rik van Riel