Re: [RFC] respect the referenced bit of KVM guest pages?

[Minchan Kim]

On Wed, Aug 19, 2009 at 9:10 PM, Wu Fengguang<fengguang.wu@xxxxxxxxx> 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
>> >
>> > Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Âmark 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.
>> >
>> > Â Â Â Â Â Â Â Â Â Â Â Â Â PG_mlocked
>> >
>> >> Otherwise vm stastics show strange number.
>> >>
>> >> This patch does that.
>> >
>> > Reviewed-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
>>
>> 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
>> >> Â Â Â Â* unevictable list.
>> >> Â Â Â Â*/
>> >> Â Â Â if (vma->vm_flags & VM_LOCKED) {
>> >> - Â Â Â Â Â Â *mapcount = 1; Â/* break early from loop */
>> >> + Â Â Â Â Â Â *mapcount = 1; Â Â Â Â Â/* break early from loop */
>> >> + Â Â Â Â Â Â *vm_flags |= VM_LOCKED; /* for prevent to move active list */
>> >
>> >> + Â Â Â Â Â Â 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 ?


>
> Thanks,
> Fengguang
>
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-- 
Kind regards,
Minchan Kim
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