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From: Matthew Wilcox <willy@infradead.org>
To: Wei Yang <richard.weiyang@gmail.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
	Wei Yang <richardw.yang@linux.intel.com>,
	akpm@linux-foundation.org, kirill.shutemov@linux.intel.com,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] mm/page_vma_mapped: page table boundary is already guaranteed
Date: Thu, 28 Nov 2019 14:39:04 -0800	[thread overview]
Message-ID: <20191128223904.GG20752@bombadil.infradead.org> (raw)
In-Reply-To: <20191128210945.6gtt7wlygsvxip4n@master>

On Thu, Nov 28, 2019 at 09:09:45PM +0000, Wei Yang wrote:
> 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 <richardw.yang@linux.intel.com>
> >
> >NAK.
> >
> >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
> unmapped.

mremap() can also move a mapping, see MREMAP_FIXED.

> 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
> guarded?
> 
> 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
> >workload.
> >
> >-- 
> > Kirill A. Shutemov
> 
> -- 
> Wei Yang
> Help you, Help me
> 


  reply	other threads:[~2019-11-28 22:39 UTC|newest]

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
2019-11-28 22:39       ` Matthew Wilcox [this message]
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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