linux-kernel - Re: [PATCH 2/2] arm64/hugetlb: Implement arm64 specific huge_ptep

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Date:   Tue, 10 May 2022 23:59:41 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc:     catalin.marinas@....com, will@...nel.org, mike.kravetz@...cle.com,
        akpm@...ux-foundation.org, willy@...radead.org,
        anshuman.khandual@....com, christophe.leroy@...roup.eu,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 2/2] arm64/hugetlb: Implement arm64 specific
 huge_ptep_get()

On Tue, May 10, 2022 at 07:12:53PM +0800, Baolin Wang wrote:
> Now we use huge_ptep_get() to get the pte value of a hugetlb page,
> however it will only return one specific pte value for the CONT-PTE
> or CONT-PMD size hugetlb on ARM64 system, which can contain seravel
> continuous pte or pmd entries with same page table attributes. And it
> will not take into account the subpages' dirty or young bits of a
> CONT-PTE/PMD size hugetlb page.
> 
> So the huge_ptep_get() is inconsistent with huge_ptep_get_and_clear(),
> which already takes account the dirty or young bits for any subpages
> in this CONT-PTE/PMD size hugetlb [1]. Meanwhile we can miss dirty or
> young flags statistics for hugetlb pages with current huge_ptep_get(),
> such as the gather_hugetlb_stats() function, and CONT-PTE/PMD hugetlb
> monitoring with DAMON.
> 
> Thus define an ARM64 specific  huge_ptep_get() implementation, that will
> take into account any subpages' dirty or young bits for CONT-PTE/PMD size
> hugetlb page, for those functions that want to check the dirty and young
> flags of a hugetlb page.
> 
> [1] https://lore.kernel.org/linux-mm/85bd80b4-b4fd-0d3f-a2e5-149559f2f387@oracle.com/
> 
> Suggested-by: Muchun Song <songmuchun@...edance.com>
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>

LGTM. Thanks for your work.

Reviewed-by: Muchun Song <songmuchun@...edance.com>