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From: Wei Yang <>
To: "Kirill A. Shutemov" <>
Cc: Wei Yang <>,,,,
Subject: Re: [PATCH 2/2] mm/page_vma_mapped: page table boundary is already guaranteed
Date: Thu, 28 Nov 2019 21:09:45 +0000
Message-ID: <20191128210945.6gtt7wlygsvxip4n@master> (raw)
In-Reply-To: <>

On Thu, Nov 28, 2019 at 11:31:43AM +0300, Kirill A. Shutemov wrote:
>On Thu, Nov 28, 2019 at 09:03:21AM +0800, Wei Yang wrote:
>> The check here is to guarantee pvmw->address iteration is limited in one
>> page table boundary. To be specific, here the address range should be in
>> one PMD_SIZE.
>> If my understanding is correct, this check is already done in the above
>> check:
>>     address >= __vma_address(page, vma) + PMD_SIZE
>> The boundary check here seems not necessary.
>> Signed-off-by: Wei Yang <>
>THP can be mapped with PTE not aligned to PMD_SIZE. Consider mremap().

Hi, Kirill

Thanks for your comment during Thanks Giving Day. Happy holiday:-)

I didn't think about this case before, thanks for reminding. Then I tried to
understand your concern.

mremap() would expand/shrink a memory mapping. In this case, probably shrink
is in concern. Since pvmw->page and pvmw->vma are not changed in the loop, the
case you mentioned maybe pvmw->page is the head of a THP but part of it is

This means the following condition stands:

    vma->vm_start <= vma_address(page) 
    vma->vm_end <=   vma_address(page) + page_size(page)

Since we have checked address with vm_end, do you think this case is also

Not sure my understanding is correct, look forward your comments.

>> Test:
>>    more than 48 hours kernel build test shows this code is not touched.
>Not an argument. I doubt mremap(2) is ever called in kernel build
> Kirill A. Shutemov

Wei Yang
Help you, Help me

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Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-28  1:03 [PATCH 1/2] mm/page_vma_mapped: use PMD_SIZE instead of calculating it Wei Yang
2019-11-28  1:03 ` [PATCH 2/2] mm/page_vma_mapped: page table boundary is already guaranteed Wei Yang
2019-11-28  8:31   ` Kirill A. Shutemov
2019-11-28 21:09     ` Wei Yang [this message]
2019-11-28 22:39       ` Matthew Wilcox
2019-11-29  8:30         ` Wei Yang
2019-11-29 11:18           ` Matthew Wilcox
2019-12-02  6:53             ` Wei Yang
2019-11-28  8:32 ` [PATCH 1/2] mm/page_vma_mapped: use PMD_SIZE instead of calculating it Kirill A. Shutemov
2019-11-28 21:22   ` Wei Yang
2019-12-02  8:03     ` Kirill A. Shutemov
2019-12-02  8:54       ` Wei Yang
2019-12-02 22:21       ` Wei Yang
2019-12-03  9:47         ` Kirill A. Shutemov
2019-12-03 15:14           ` Wei Yang

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