From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with ESMTP id 9156E9000BD for ; Mon, 26 Sep 2011 10:55:11 -0400 (EDT) Received: by wyf22 with SMTP id 22so6966784wyf.14 for ; Mon, 26 Sep 2011 07:55:08 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20110926142540.GE14333@redhat.com> References: <1316948380-1879-1-git-send-email-consul.kautuk@gmail.com> <20110926112944.GC14333@redhat.com> <20110926142540.GE14333@redhat.com> Date: Mon, 26 Sep 2011 20:25:06 +0530 Message-ID: Subject: Re: [patch] mm: remove sysctl to manually rescue unevictable pages From: "kautuk.c @samsung.com" Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Andrew Morton , Mel Gorman , Minchan Kim , KAMEZAWA Hiroyuki , Rik van Riel , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Lee Schermerhorn , KOSAKI Motohiro On Mon, Sep 26, 2011 at 7:55 PM, Johannes Weiner wrote= : > On Mon, Sep 26, 2011 at 05:59:39PM +0530, kautuk.c @samsung.com wrote: >> On Mon, Sep 26, 2011 at 5:40 PM, kautuk.c @samsung.com >> wrote: >> > On Mon, Sep 26, 2011 at 4:59 PM, Johannes Weiner = wrote: >> >> On Sun, Sep 25, 2011 at 04:29:40PM +0530, Kautuk Consul wrote: >> >>> write_scan_unavictable_node checks the value req returned by >> >>> strict_strtoul and returns 1 if req is 0. >> >>> >> >>> However, when strict_strtoul returns 0, it means successful conversi= on >> >>> of buf to unsigned long. >> >>> >> >>> Due to this, the function was not proceeding to scan the zones for >> >>> unevictable pages even though we write a valid value to the >> >>> scan_unevictable_pages sys file. >> >> >> >> Given that there is not a real reason for this knob (anymore) and tha= t >> >> it apparently never really worked since the day it was introduced, ho= w >> >> about we just drop all that code instead? >> >> >> >> =A0 =A0 =A0 =A0Hannes >> >> >> >> --- >> >> From: Johannes Weiner >> >> Subject: mm: remove sysctl to manually rescue unevictable pages >> >> >> >> At one point, anonymous pages were supposed to go on the unevictable >> >> list when no swap space was configured, and the idea was to manually >> >> rescue those pages after adding swap and making them evictable again. >> >> But nowadays, swap-backed pages on the anon LRU list are not scanned >> >> without available swap space anyway, so there is no point in moving >> >> them to a separate list anymore. >> > >> > Is this code only for anonymous pages ? >> > It seems to look at all pages in the zone both file as well as anon. >> > >> >> >> >> The manual rescue could also be used in case pages were stranded on >> >> the unevictable list due to race conditions. =A0But the code has been >> >> around for a while now and newly discovered bugs should be properly >> >> reported and dealt with instead of relying on such a manual fixup. >> > >> > What you say seems to be all right for anon pages, but what about file >> > pages ? >> > I'm not sure about how this could happen, but what if some file-system= caused >> > a file cache page to be set to evictable or reclaimable without >> > actually removing >> > that page from the unevictable list ? >> >> What I would like to also add is that while the transition of an anon >> page from and >> to the unevictable lists is straight-forward, should we make the same as= sumption >> about file cache pages ? > > We should make no assumptions if our code base is open source :-) > >> I am not sure about this, but could a file-system cause this kind of a p= roblem >> independent of the mlocking behaviour of a user-mode app ? > > Currently, I only see shmem and ramfs meddling with unevictability > outside of mlock and they both look correct to me. > > I'd say that if a filesystem required this knob and user-intervention > for the VM to behave correctly, it needs fixing. Yes I agree. Otherwise that kind of defeats the overall purpose of open-source. :) Thanks for review and the info. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org