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Subject: Re: [RFC] respect the referenced bit of KVM guest pages?
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Minchan Kim <minchan.kim@gmail.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>, Rik van Riel <riel@redhat.com>,
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       "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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>> Hmm, I think
>>
>> 1. Anyway, we need turn on PG_mlock.
>
> I add my patch again to explain.
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index ed63894..283266c 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -358,6 +358,7 @@ static int page_referenced_one(struct page *page,
>         */
>        if (vma->vm_flags & VM_LOCKED) {
>                *mapcount = 1;  /* break early from loop */
> +               *vm_flags |= VM_LOCKED;
>                goto out_unmap;
>        }
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index d224b28..d156e1d 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -632,7 +632,8 @@ static unsigned long shrink_page_list(struct
> list_head *page_list,
>                                                sc->mem_cgroup, &vm_flags);
>                /* In active use or really unfreeable?  Activate it. */
>                if (sc->order <= PAGE_ALLOC_COSTLY_ORDER &&
> -                                       referenced && page_mapping_inuse(page))
> +                                       referenced && page_mapping_inuse(page)
> +                                       && !(vm_flags & VM_LOCKED))
>                        goto activate_locked;
>
> By this check, the page can be reached at try_to_unmap after
> page_referenced in shrink_page_list. At that time PG_mlocked will be
> set.

You are right.
Please add my Reviewed-by sign to your patch.

Thanks.