From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755380AbaCNQGh (ORCPT ); Fri, 14 Mar 2014 12:06:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56063 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755312AbaCNQGg (ORCPT ); Fri, 14 Mar 2014 12:06:36 -0400 Message-ID: <53232901.5030307@redhat.com> Date: Fri, 14 Mar 2014 12:06:25 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Johannes Weiner , Andrew Morton CC: Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [patch] mm: vmscan: do not swap anon pages just because free+file is low References: <1394811302-30468-1-git-send-email-hannes@cmpxchg.org> In-Reply-To: <1394811302-30468-1-git-send-email-hannes@cmpxchg.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/14/2014 11:35 AM, Johannes Weiner wrote: > Page reclaim force-scans / swaps anonymous pages when file cache drops > below the high watermark of a zone in order to prevent what little > cache remains from thrashing. > > However, on bigger machines the high watermark value can be quite > large and when the workload is dominated by a static anonymous/shmem > set, the file set might just be a small window of used-once cache. In > such situations, the VM starts swapping heavily when instead it should > be recycling the no longer used cache. > > This is a longer-standing problem, but it's more likely to trigger > after 81c0a2bb515f ("mm: page_alloc: fair zone allocator policy") > because file pages can no longer accumulate in a single zone and are > dispersed into smaller fractions among the available zones. > > To resolve this, do not force scan anon when file pages are low but > instead rely on the scan/rotation ratios to make the right prediction. I am not entirely sure that the scan/rotation ratio will be meaningful when the page cache has been essentially depleted, but on larger systems the distance between the low and high watermark is gigantic, and I have no better idea on how to fix the bug you encountered, so ... > Signed-off-by: Johannes Weiner > Cc: [3.12+] Reviewed-by: Rik van Riel -- All rights reversed