linux-kernel - Re: [PATCH] mm: mempolicy: Skip inaccessible VMAs when setting MPOL_MF

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Date:	Thu, 2 Oct 2014 12:41:30 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Mel Gorman <mgorman@...e.de>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Hugh Dickins <hughd@...gle.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH] mm: mempolicy: Skip inaccessible VMAs when setting
 MPOL_MF_LAZY

On Thu, 2 Oct 2014, Mel Gorman wrote:

> PROT_NUMA VMAs are skipped to avoid problems distinguishing between
> present, prot_none and special entries. MPOL_MF_LAZY is not visible from
> userspace since commit a720094ded8c ("mm: mempolicy: Hide MPOL_NOOP and
> MPOL_MF_LAZY from userspace for now") but it should still skip VMAs the
> same way task_numa_work does.
> 
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> Acked-by: Rik van Riel <riel@...hat.com>

Acked-by: Hugh Dickins <hughd@...gle.com>

Yes, this is much the same as the patch I wrote for Linus two days ago,
then discovered that we don't need until MPOL_MF_LAZY gets brought back
into MPOL_MF_VALID.  (As a bonus, my patch did also remove the currently
bogus paragraph of comment above change_prot_numa(); and I would prefer a
code comment to make clear that we never exercise this path at present.) 

> ---
>  mm/mempolicy.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 8f5330d..a5877ce 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -683,7 +683,9 @@ queue_pages_range(struct mm_struct *mm, unsigned long start, unsigned long end,
>  		}
>  
>  		if (flags & MPOL_MF_LAZY) {
> -			change_prot_numa(vma, start, endvma);
> +			/* Similar to task_numa_work, skip inaccessible VMAs */
> +			if (vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))
> +				change_prot_numa(vma, start, endvma);
>  			goto next;
>  		}
>  
--
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