linux-kernel - Re: [PATCH] mm:mempolicy: skip VM_HUGETLB and VM

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Date:	Tue, 19 Jan 2016 10:12:57 +0900 (KST)
From:	SeongJae Park <sj38.park@...il.com>
To:	Liang Chen <liangchen.linux@...il.com>
cc:	n-horiguchi@...jp.nec.com, linux-mm@...ck.org, riel@...hat.com,
	mgorman@...e.de, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, Gavin Guo <gavin.guo@...onical.com>
Subject: Re: [PATCH] mm:mempolicy: skip VM_HUGETLB and VM_MIXEDMAP VMA for
 lazy mbind

Hello Liang,

Just trivial comment below.

On Mon, 18 Jan 2016, Liang Chen wrote:

> VM_HUGETLB and VM_MIXEDMAP vma needs to be excluded to avoid compound
> pages being marked for migration and unexpected COWs when handling
> hugetlb fault.
>
> Thanks to Naoya Horiguchi for reminding me on these checks.
>
> Signed-off-by: Liang Chen <liangchen.linux@...il.com>
> Signed-off-by: Gavin Guo <gavin.guo@...onical.com>
> ---
> mm/mempolicy.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 436ff411..415de70 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -610,8 +610,9 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
>
> 	if (flags & MPOL_MF_LAZY) {
> 		/* Similar to task_numa_work, skip inaccessible VMAs */
> -		if (vma_migratable(vma) &&
> -			vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))
> +		if (vma_migratable(vma) && !is_vm_hugetlb_page(vma) &&
> +			(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)) &&
> +			!(vma->vm_flags & VM_MIXEDMAP))

Isn't there exists few unnecessary parenthesis? IMHO, it makes me hard to 
read the code.

How about below code, instead?

+             if (vma_migratable(vma) && !is_vm_hugetlb_page(vma) &&
+                     vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE) &&
+                     !vma->vm_flags & VM_MIXEDMAP)


Thanks,
SeongJae Park.

> 			change_prot_numa(vma, start, endvma);
> 		return 1;
> 	}
> -- 
> 1.9.1
>
> --
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