From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id E6F136B004D for ; Wed, 19 Aug 2009 10:01:11 -0400 (EDT) Date: Wed, 19 Aug 2009 22:00:53 +0800 From: Wu Fengguang Subject: Re: [RFC] respect the referenced bit of KVM guest pages? Message-ID: <20090819140053.GA7628@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> <28c262360908190638g521e55bcje14cb321c9a22c51@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <28c262360908190638g521e55bcje14cb321c9a22c51@mail.gmail.com> Sender: owner-linux-mm@kvack.org To: Minchan Kim 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 List-ID: On Wed, Aug 19, 2009 at 09:38:05PM +0800, Minchan Kim wrote: > 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 > >> >> > > >> >> > A A A A A A A A A A A A A A A A A A A A A A A A A A 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. > >> >> > > >> >> > A A A A A A A A A A A A A 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 A A A 2009-08-18 19:48:14.000000000 +0900 > >> >> >> +++ b/mm/rmap.c A A A 2009-08-18 23:47:34.000000000 +0900 > >> >> >> @@ -362,7 +362,9 @@ static int page_referenced_one(struct pa > >> >> >> A A A A * unevictable list. > >> >> >> A A A A */ > >> >> >> A A A if (vma->vm_flags & VM_LOCKED) { > >> >> >> - A A A A A A *mapcount = 1; A /* break early from loop */ > >> >> >> + A A A A A A *mapcount = 1; A A A A A /* break early from loop */ > >> >> >> + A A A A A A *vm_flags |= VM_LOCKED; /* for prevent to move active list */ > >> >> > > >> >> >> + A A A A A A 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. Yes, indeed! > > - the "if (VM_LOCKED) referenced = 0" in page_referenced() could > > A 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. The active list case can be persistent, when the mlocked (but without PG_mlocked) page is executable and referenced by 2+ processes. But I admit that executable pages are relatively rare. > 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. :) Now you decide :) Thanks, Fengguang > > I did like your proposed > > > > A A A A A A A A if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && > > - A A A A A A A A A A A A A A A A A A A referenced && page_mapping_inuse(page)) > > + A A A A A A A A A A A A A A A A A A A referenced && page_mapping_inuse(page) > > + A A A A A A A A A A A A A A A A A A A && !(vm_flags & VM_LOCKED)) > > A A A A A A A A A A A A goto activate_locked; > > > > which looks more intuitive and less confusing. > > > > Thanks, > > Fengguang > > > > > > -- > Kind regards, > Minchan Kim -- 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/ . 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