From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f173.google.com (mail-we0-f173.google.com [74.125.82.173]) by kanga.kvack.org (Postfix) with ESMTP id 548056B0070 for ; Fri, 14 Mar 2014 12:06:36 -0400 (EDT) Received: by mail-we0-f173.google.com with SMTP id w61so2286750wes.4 for ; Fri, 14 Mar 2014 09:06:35 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTP id en20si9104055wic.72.2014.03.14.09.06.33 for ; Fri, 14 Mar 2014 09:06:34 -0700 (PDT) Message-ID: <53232901.5030307@redhat.com> Date: Fri, 14 Mar 2014 12:06:25 -0400 From: Rik van Riel MIME-Version: 1.0 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: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner , Andrew Morton Cc: Mel Gorman , linux-mm@kvack.org, 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 -- 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