From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752304AbZHSNiH (ORCPT ); Wed, 19 Aug 2009 09:38:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751843AbZHSNiG (ORCPT ); Wed, 19 Aug 2009 09:38:06 -0400 Received: from mail-yx0-f175.google.com ([209.85.210.175]:36168 "EHLO mail-yx0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751746AbZHSNiE convert rfc822-to-8bit (ORCPT ); Wed, 19 Aug 2009 09:38:04 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=LAhAKoF6jWl+/yjQ/koEhNuHLF8jrCT8HmupqzIciY1XG6WAWeHGWwm9oi8GC19po2 STWfpTPGn+5GYR0Rdne/9Qw1voPmd+ftzsxqoqLReWJ15cM+lLS7K1AMBmPru2GEga5R x6fejOnYX7UAuS47SOHaNX7XObXRC0BbveYZ4= MIME-Version: 1.0 In-Reply-To: <20090819132420.GA6137@localhost> References: <20090816051502.GB13740@localhost> <20090816112910.GA3208@localhost> <20090818234310.A64B.A69D9226@jp.fujitsu.com> <20090819120117.GB7306@localhost> <2f11576a0908190505h6da96280xf67c962aa3f5ba07@mail.gmail.com> <20090819121017.GA8226@localhost> <28c262360908190525i6e56ead0mb8dcb01c3d1a69f1@mail.gmail.com> <20090819132420.GA6137@localhost> Date: Wed, 19 Aug 2009 22:38:05 +0900 Message-ID: <28c262360908190638g521e55bcje14cb321c9a22c51@mail.gmail.com> Subject: Re: [RFC] respect the referenced bit of KVM guest pages? From: Minchan Kim To: Wu Fengguang Cc: KOSAKI Motohiro , Rik van Riel , Jeff Dike , Avi Kivity , Andrea Arcangeli , "Yu, Wilfred" , "Kleen, Andi" , Hugh Dickins , Andrew Morton , Christoph Lameter , Mel Gorman , LKML , linux-mm Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 19, 2009 at 10:24 PM, Wu Fengguang wrote: > On Wed, Aug 19, 2009 at 08:25:56PM +0800, Minchan Kim wrote: >> On Wed, Aug 19, 2009 at 9:10 PM, Wu Fengguang wrote: >> > On Wed, Aug 19, 2009 at 08:05:19PM +0800, KOSAKI Motohiro wrote: >> >> >> page_referenced_file? >> >> >> I think we should change page_referenced(). >> >> > >> >> > Yeah, good catch. >> >> > >> >> >> >> >> >> Instead, How about this? >> >> >> ============================================== >> >> >> >> >> >> Subject: [PATCH] mm: stop circulating of referenced mlocked pages >> >> >> >> >> >> Currently, mlock() systemcall doesn't gurantee to mark the page PG_Mlocked >> >> > >> >> >                                                    mark PG_mlocked >> >> > >> >> >> because some race prevent page grabbing. >> >> >> In that case, instead vmscan move the page to unevictable lru. >> >> >> >> >> >> However, Recently Wu Fengguang pointed out current vmscan logic isn't so >> >> >> efficient. >> >> >> mlocked page can move circulatly active and inactive list because >> >> >> vmscan check the page is referenced _before_ cull mlocked page. >> >> >> >> >> >> Plus, vmscan should mark PG_Mlocked when cull mlocked page. >> >> > >> >> >                           PG_mlocked >> >> > >> >> >> Otherwise vm stastics show strange number. >> >> >> >> >> >> This patch does that. >> >> > >> >> > Reviewed-by: Wu Fengguang >> >> >> >> Thanks. >> >> >> >> >> >> >> >> >> Index: b/mm/rmap.c >> >> >> =================================================================== >> >> >> --- a/mm/rmap.c       2009-08-18 19:48:14.000000000 +0900 >> >> >> +++ b/mm/rmap.c       2009-08-18 23:47:34.000000000 +0900 >> >> >> @@ -362,7 +362,9 @@ static int page_referenced_one(struct pa >> >> >>        * unevictable list. >> >> >>        */ >> >> >>       if (vma->vm_flags & VM_LOCKED) { >> >> >> -             *mapcount = 1;  /* break early from loop */ >> >> >> +             *mapcount = 1;          /* break early from loop */ >> >> >> +             *vm_flags |= VM_LOCKED; /* for prevent to move active list */ >> >> > >> >> >> +             try_set_page_mlocked(vma, page); >> >> > >> >> > That call is not absolutely necessary? >> >> >> >> Why? I haven't catch your point. >> > >> > Because we'll eventually hit another try_set_page_mlocked() when >> > trying to unmap the page. Ie. duplicated with another call you added >> > in this patch. >> >> Yes. we don't have to call it and we can make patch simple. >> I already sent patch on yesterday. >> >> http://marc.info/?l=linux-mm&m=125059325722370&w=2 >> >> I think It's more simple than KOSAKI's idea. >> Is any problem in my patch ? > > No, IMHO your patch is simple and good, while KOSAKI's is more > complete :) > > - the try_set_page_mlocked() rename is suitable > - the call to try_set_page_mlocked() is necessary on try_to_unmap() We don't need try_set_page_mlocked call in try_to_unmap. That's because try_to_unmap_xxx will call try_to_mlock_page if the page is included in any VM_LOCKED vma. Eventually, It can move unevictable list. > - the "if (VM_LOCKED) referenced = 0" in page_referenced() could >  cover both active/inactive vmscan ASAP we set PG_mlocked in page, we can save unnecessary vmscan cost from active list to inactive list. But I think it's rare case so that there would be few pages. So I think that will be not big overhead. As I know, Rescue by vmscan page losing the isolation race was the Lee's design. But as you pointed out, it have a bug that vmscan can't rescue the page due to reach try_to_unmap. So I think this approach is proper. :) > I did like your proposed > >                if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && > -                                       referenced && page_mapping_inuse(page)) > +                                       referenced && page_mapping_inuse(page) > +                                       && !(vm_flags & VM_LOCKED)) >                        goto activate_locked; > > which looks more intuitive and less confusing. > > Thanks, > Fengguang > -- Kind regards, Minchan Kim