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Subject: Re: [RFC] respect the referenced bit of KVM guest pages?
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Rik van Riel <riel@redhat.com>, Jeff Dike <jdike@addtoit.com>,
       Avi Kivity <avi@redhat.com>, Andrea Arcangeli <aarcange@redhat.com>,
       "Yu, Wilfred" <wilfred.yu@intel.com>,
       "Kleen, Andi" <andi.kleen@intel.com>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>,
       Andrew Morton <akpm@linux-foundation.org>,
       Christoph Lameter <cl@linux-foundation.org>, Mel Gorman <mel@csn.ul.ie>,
       LKML <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>
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>> 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 <fengguang.wu@intel.com>

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.