linux-kernel - Re: [PATCH 0/2] don't use mapcount() to check large folio sharing

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Date:   Fri, 4 Aug 2023 15:14:53 +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 0/2] don't use mapcount() to check large folio sharing

Hi Andrew,

On 8/2/2023 8:39 PM, Yin, Fengwei wrote:
> Hi Andrew,
> 
> On 7/29/2023 1:24 AM, Andrew Morton wrote:
>> On Sat, 29 Jul 2023 00:13:54 +0800 Yin Fengwei <fengwei.yin@...el.com> wrote:
>>
>>> In madvise_cold_or_pageout_pte_range() and madvise_free_pte_range(),
>>> folio_mapcount() is used to check whether the folio is shared. But it's
>>> not correct as folio_mapcount() returns total mapcount of large folio.
>>>
>>> Use folio_estimated_sharers() here as the estimated number is enough.
>>
>> What are the user-visible runtime effects of these changes?
>>
>> (and please try to avoid using the same Subject: for different patches)
>>
> 
> Can you hold on these patches to mm-unstable? I think we need to wait for
> David's work on folio_maybe_mapped_shared() and redo the fix base on that.
> Thanks and sorry for the noise.
Sorry for bothering you again for this patchset.

Let me explain the situation here:
  - The reason to hold on the patches to mm-unstable is that I don't want to
    promote the fix in this patch (using folio_estimated_sharers()). The
    correct way is waiting for folio_maybe_mapped_shared() from David.

    Merging these patches motivate using folio_estimated_sharers() in other
    places. So once folio_maybe_mapped_shared() is ready, we need to replace
    folio_estimated_sharers() with folio_maybe_mapped_shared().

  - For this specific patches, if they are suitable for stable, we may want to
    merge it (special for stable branch. I assume folio_maybe_mapped_shared()
    may not be back ported to stable branch).

So how do we deal with this situation? Thanks in advance.

Regards
Yin, Fengwei

> 
> 
> Regards
> Yin, Fengwei