From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id EC2276B004D for ; Mon, 22 Feb 2010 15:34:29 -0500 (EST) Message-ID: <4B82EA4D.8040305@redhat.com> Date: Mon, 22 Feb 2010 15:34:21 -0500 From: Rik van Riel MIME-Version: 1.0 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: owner-linux-mm@kvack.org To: Johannes Weiner Cc: Andrew Morton , KOSAKI Motohiro , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org