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Date: Tue, 18 Aug 2009 10:34:38 +0800 From: Wu Fengguang <fengguang.wu@...el.com> To: Minchan Kim <minchan.kim@...il.com> Cc: Rik van Riel <riel@...hat.com>, Jeff Dike <jdike@...toit.com>, Avi Kivity <avi@...hat.com>, Andrea Arcangeli <aarcange@...hat.com>, "Yu, Wilfred" <wilfred.yu@...el.com>, "Kleen, Andi" <andi.kleen@...el.com>, Hugh Dickins <hugh.dickins@...cali.co.uk>, Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...ux-foundation.org>, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, Mel Gorman <mel@....ul.ie>, LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org> Subject: Re: [RFC] respect the referenced bit of KVM guest pages? 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<fengguang.wu@...el.com> 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 - > >> > >> Is there a good reason for this to be in shrink_active_list() > >> > >> as opposed to __isolate_lru_page? > >> > >> > >> > >> if (unlikely(!page_evictable(page, NULL))) { > >> > >> putback_lru_page(page); > >> > >> continue; > >> > >> } > >> > >> > >> > >> 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 <fengguang.wu@...el.com> > > --- > > > > --- linux.orig/mm/rmap.c 2009-08-16 19:11:13.000000000 +0800 > > +++ linux/mm/rmap.c 2009-08-16 19:22:46.000000000 +0800 > > @@ -358,6 +358,7 @@ static int page_referenced_one(struct pa > > */ > > if (vma->vm_flags & VM_LOCKED) { > > *mapcount = 1; /* break early from loop */ > > + *vm_flags |= VM_LOCKED; > > goto out_unmap; > > } > > > > @@ -482,6 +483,8 @@ static int page_referenced_file(struct p > > } > > > > spin_unlock(&mapping->i_mmap_lock); > > + if (*vm_flags & VM_LOCKED) > > + referenced = 0; > > return referenced; > > } > > > > > > -- > > To unsubscribe, send a message with 'unsubscribe linux-mm' in > > the body to majordomo@...ck.org. For more info on Linux MM, > > see: http://www.linux-mm.org/ . > > Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a> > > > > > > -- > Kind regards, > Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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