linux-kernel - Re: [PATCH][mm] adjust the logic of checking THP

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Message-ID: <CAGW+__+=q6W92+0HZWeQsqKt+wiBu7sPU8jTOxbaR_JEfqo6Qw@mail.gmail.com>
Date:	Thu, 3 Nov 2011 10:19:21 +0800
From:	GuanJun He <heguanbo@...il.com>
To:	Hillf Danton <dhillf@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH][mm] adjust the logic of checking THP

On Wed, Nov 2, 2011 at 8:17 PM, Hillf Danton <dhillf@...il.com> wrote:
> On Wed, Nov 2, 2011 at 2:34 PM, Guanjun He <heguanbo@...il.com> wrote:
>>
>> Acturally, pmd_trans_huge(orig_pmd) only checks the _PAGE_PSE bits,
>> it's a pmd entry bits, only mark a size, not a flag;As one can easily
>> create the same pmd entry bits for some special use,then the check
>> will get confused.And this patch is to adjust the logic to use the flag,
>> it can perfectly avoid this potential issuse,and basically no impact
>> to the current code.
>>
>>
>> Signed-off-by: Guanjun He <heguanbo@...il.com>
>> ---
>>  mm/memory.c |   28 +++++++++++++++-------------
>>  1 files changed, 15 insertions(+), 13 deletions(-)
>>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index a56e3ba..a76b17f 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -3465,20 +3465,22 @@ int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>>        pmd = pmd_alloc(mm, pud, address);
>>        if (!pmd)
>>                return VM_FAULT_OOM;
>> -       if (pmd_none(*pmd) && transparent_hugepage_enabled(vma)) {
>> -               if (!vma->vm_ops)
>> -                       return do_huge_pmd_anonymous_page(mm, vma, address,
>> -                                                         pmd, flags);
>> -       } else {
>> -               pmd_t orig_pmd = *pmd;
>> -               barrier();
>> -               if (pmd_trans_huge(orig_pmd)) {
>> -                       if (flags & FAULT_FLAG_WRITE &&
>> -                           !pmd_write(orig_pmd) &&
>> -                           !pmd_trans_splitting(orig_pmd))
>> -                               return do_huge_pmd_wp_page(mm, vma, address,
>> -                                                          pmd, orig_pmd);
>> +       if (transparent_hugepage_enabled(vma)) {
>
> Well, how about THP not configured?

What do you mean 'not configured'? assume not enabled.
If THP not enabled, of course the transparent_hugepage_enabled(vma)
will be false.

>
> Thanks,
>              Hillf
>
>> +               if (pmd_none(*pmd)) {
>> +                       if (!vma->vm_ops)
>> +                               return do_huge_pmd_anonymous_page(mm, vma, address,
>> +                                                                 pmd, flags);
>> +               } else {
>> +                       pmd_t orig_pmd = *pmd;
>> +                       barrier();
>> +                       if (pmd_trans_huge(orig_pmd)) {
>> +                               if (flags & FAULT_FLAG_WRITE &&
>> +                                   !pmd_write(orig_pmd) &&
>> +                                   !pmd_trans_splitting(orig_pmd))
>> +                                       return do_huge_pmd_wp_page(mm, vma, address,
>> +                                                                  pmd, orig_pmd);
>>                        return 0;
>> +                       }
>>                }
>>        }
>>
>> --
>> 1.7.7
>>
>> --
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>>
>
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