linux-kernel - Re: [PATCH 2/2] madvise: don't use mapcount() against large folio for sharing check

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Message-ID: <24e7429c-14ed-d953-e652-eac178de76e3@intel.com>
Date:   Sat, 29 Jul 2023 21:53:08 +0800
From:   "Yin, Fengwei" <fengwei.yin@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <stable@...r.kernel.org>, <willy@...radead.org>,
        <vishal.moola@...il.com>, <wangkefeng.wang@...wei.com>,
        <minchan@...nel.org>, <yuzhao@...gle.com>, <david@...hat.com>,
        <ryan.roberts@....com>, <shy828301@...il.com>
Subject: Re: [PATCH 2/2] madvise: don't use mapcount() against large folio for
 sharing check

Hi Andrew,

On 7/29/2023 1:41 AM, Andrew Morton wrote:
> On Sat, 29 Jul 2023 00:13:56 +0800 Yin Fengwei <fengwei.yin@...el.com> wrote:
> 
>> Fixes: 98b211d6415f ("madvise: convert madvise_free_pte_range() to use a folio")
>> Fixes: fc986a38b670 ("mm: huge_memory: convert madvise_free_huge_pmd to use a folio")
> 
> Having two Fixes: for one patch presumably makes backporting more
> complicated and adds risk of making mistakes.
> 
> So I have split this into a three-patch series and I've fixed up the patch naming:
> 
> Subject: madvise:madvise_cold_or_pageout_pte_range(): don't use mapcount() against large folio for sharing check
> Subject: madvise:madvise_free_huge_pmd(): don't use mapcount() against large folio for sharing check
> Subject: madvise:madvise_free_pte_range(): don't use mapcount() against large folio for sharing check
Thanks a lot for your kind help. Will be careful for the future patches.

> 
> I haven't added cc:stable at this time - that awaits the description of
> user-visible effects.
The impact of the patch:
  Without the patch, when user calls madvise() with MADV_COLD, MADV_PAGEOUT
  and MADV_FREE, it's likely THP pages will be skipped. With the patch,
  It's likely the THP pages will be split to pages which will be made code,
  reclaimed and freed.


Regards
Yin, Fengwei