Re: [PATCH] mm:mempolicy: skip VM_HUGETLB and VM_MIXEDMAP VMA for lazy mbind

[Gavin Guo <gavin.guo@canonical.com>]

Hi SeongJae,

On Tue, Jan 19, 2016 at 9:12 AM, SeongJae Park <sj38.park@gmail.com> wrote:
> 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@gmail.com>
>> Signed-off-by: Gavin Guo <gavin.guo@canonical.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) &&

Thanks for your suggestion, it's good for the above. However, it should be
a typo for the following and I think you mean:

        ~vma->vm_flags & VM_MIXEDMAP

Even though the result is correct, I feel it's a bit of ambiguous for
people to understand and away from it's original meaning.

> +                     !vma->vm_flags & VM_MIXEDMAP)
>
>
> Thanks,
> SeongJae Park.
>
>>                         change_prot_numa(vma, start, endvma);
>>                 return 1;
>>         }
>> --
>> 1.9.1
>>
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