linux-kernel - Re: [PATCH v2 2/5] mm: damon must atomically clear young on ptes and pmds

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Date:   Fri, 19 May 2023 09:53:42 +0100
From:   Ryan Roberts <ryan.roberts@....com>
To:     SeongJae Park <sj@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Uladzislau Rezki <urezki@...il.com>, Zi Yan <ziy@...dia.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        damon@...ts.linux.dev
Subject: Re: [PATCH v2 2/5] mm: damon must atomically clear young on ptes and
 pmds

On 18/05/2023 18:13, SeongJae Park wrote:
> Hi Ryan,
> 
> 
> Nit.  For consistency of DAMON commits subjects, I'd prefer something like
> "mm/damon/ops-common: atomically test and clear young on ptes and pmds".
> 
> On Thu, 18 May 2023 12:07:24 +0100 Ryan Roberts <ryan.roberts@....com> wrote:
> 
>> It is racy to non-atomically read a pte, then clear the young bit, then
>> write it back as this could discard dirty information. Further, it is
>> bad practice to directly set a pte entry within a table. Instead
>> clearing young must go through the arch-provided helper,
>> ptep_test_and_clear_young() to ensure it is modified atomically and to
>> give the arch code visibility and allow it to check (and potentially
>> modify) the operation.
>>
>> Fixes: 46c3a0accdc4 ("mm/damon/vaddr: separate commonly usable functions")
> 
> Nit.  The commit is only for refactoring.  The original code camde from commit
> 3f49584b262c ("mm/damon: implement primitives for the virtual memory address
> spaces").
> 
>> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
>> Reviewed-by: Zi Yan <ziy@...dia.com>
> 
> Other than above nits,
> 
> Reviewed-by: SeongJae Park <sj@...nel.org>

Thanks for the reviews! I'll fix the nits you raised for v3.

> 
> 
> Thanks,
> SJ
>