From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id D44216B004D for ; Mon, 17 Aug 2009 22:34:41 -0400 (EDT) Date: Tue, 18 Aug 2009 10:34:38 +0800 From: Wu Fengguang Subject: Re: [RFC] respect the referenced bit of KVM guest pages? Message-ID: <20090818023438.GB7958@localhost> References: <20090806102057.GQ23385@random.random> <20090806105932.GA1569@localhost> <4A7AC201.4010202@redhat.com> <20090806130631.GB6162@localhost> <20090806210955.GA14201@c2.user-mode-linux.org> <20090816031827.GA6888@localhost> <4A87829C.4090908@redhat.com> <20090816051502.GB13740@localhost> <20090816112910.GA3208@localhost> <28c262360908170733q4bc5ddb8ob2fc976b6a468d6e@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <28c262360908170733q4bc5ddb8ob2fc976b6a468d6e@mail.gmail.com> Sender: owner-linux-mm@kvack.org To: Minchan Kim Cc: Rik van Riel , Jeff Dike , Avi Kivity , Andrea Arcangeli , "Yu, Wilfred" , "Kleen, Andi" , Hugh Dickins , Andrew Morton , Christoph Lameter , KOSAKI Motohiro , Mel Gorman , LKML , linux-mm List-ID: Minchan, On Mon, Aug 17, 2009 at 10:33:54PM +0800, Minchan Kim wrote: > On Sun, Aug 16, 2009 at 8:29 PM, Wu Fengguang wrote: > > On Sun, Aug 16, 2009 at 01:15:02PM +0800, Wu Fengguang wrote: > >> On Sun, Aug 16, 2009 at 11:53:00AM +0800, Rik van Riel wrote: > >> > Wu Fengguang wrote: > >> > > On Fri, Aug 07, 2009 at 05:09:55AM +0800, Jeff Dike wrote: > >> > >> Side question - > >> > >> A Is there a good reason for this to be in shrink_active_list() > >> > >> as opposed to __isolate_lru_page? > >> > >> > >> > >> A A A A A if (unlikely(!page_evictable(page, NULL))) { > >> > >> A A A A A A A A A putback_lru_page(page); > >> > >> A A A A A A A A A continue; > >> > >> A A A A A } > >> > >> > >> > >> Maybe we want to minimize the amount of code under the lru lock or > >> > >> avoid duplicate logic in the isolate_page functions. > >> > > > >> > > I guess the quick test means to avoid the expensive page_referenced() > >> > > call that follows it. But that should be mostly one shot cost - the > >> > > unevictable pages are unlikely to cycle in active/inactive list again > >> > > and again. > >> > > >> > Please read what putback_lru_page does. > >> > > >> > It moves the page onto the unevictable list, so that > >> > it will not end up in this scan again. > >> > >> Yes it does. I said 'mostly' because there is a small hole that an > >> unevictable page may be scanned but still not moved to unevictable > >> list: when a page is mapped in two places, the first pte has the > >> referenced bit set, the _second_ VMA has VM_LOCKED bit set, then > >> page_referenced() will return 1 and shrink_page_list() will move it > >> into active list instead of unevictable list. Shall we fix this rare > >> case? > > I think it's not a big deal. Maybe, otherwise I should bring up this issue long time before :) > As you mentioned, it's rare case so there would be few pages in active > list instead of unevictable list. Yes. > When next time to scan comes, we can try to move the pages into > unevictable list, again. Will PG_mlocked be set by then? Otherwise the situation is not likely to change and the VM_LOCKED pages may circulate in active/inactive list for countless times. > As I know about mlock pages, we already had some races condition. > They will be rescued like above. Thanks, Fengguang > > > > How about this fix? > > > > --- > > mm: stop circulating of referenced mlocked pages > > > > Signed-off-by: Wu Fengguang > > --- > > > > --- linux.orig/mm/rmap.c A A A A 2009-08-16 19:11:13.000000000 +0800 > > +++ linux/mm/rmap.c A A 2009-08-16 19:22:46.000000000 +0800 > > @@ -358,6 +358,7 @@ static int page_referenced_one(struct pa > > A A A A */ > > A A A A if (vma->vm_flags & VM_LOCKED) { > > A A A A A A A A *mapcount = 1; A /* break early from loop */ > > + A A A A A A A *vm_flags |= VM_LOCKED; > > A A A A A A A A goto out_unmap; > > A A A A } > > > > @@ -482,6 +483,8 @@ static int page_referenced_file(struct p > > A A A A } > > > > A A A A spin_unlock(&mapping->i_mmap_lock); > > + A A A if (*vm_flags & VM_LOCKED) > > + A A A A A A A referenced = 0; > > A A A A return referenced; > > A } > > > > > > -- > > To unsubscribe, send a message with 'unsubscribe linux-mm' in > > the body to majordomo@kvack.org. A For more info on Linux MM, > > see: http://www.linux-mm.org/ . > > Don't email: email@kvack.org > > > > > > -- > 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/ . Don't email: email@kvack.org