linux-kernel - Re: [PATCH 2/2] mm/page_vma_mapped: page table boundary is already guaranteed

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Message-ID: <20191128083143.kwih655snxqa2qnm@box.shutemov.name>
Date:   Thu, 28 Nov 2019 11:31:43 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm/page_vma_mapped: page table boundary is already
 guaranteed

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@...ux.intel.com>

NAK.

THP can be mapped with PTE not aligned to PMD_SIZE. Consider mremap().

> 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