linux-kernel - Re: [PATCH v2 1/1] mm/vmscan: avoid split PMD-mapped THP during shrink_folio

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Message-Id: <20240424142009.149eb988cca33822ce0fd0f1@linux-foundation.org>
Date: Wed, 24 Apr 2024 14:20:09 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Lance Yang <ioworker0@...il.com>
Cc: Matthew Wilcox <willy@...radead.org>, maskray@...gle.com,
 ziy@...dia.com, ryan.roberts@....com, david@...hat.com, 21cnbao@...il.com,
 mhocko@...e.com, fengwei.yin@...el.com, zokeefe@...gle.com,
 shy828301@...il.com, xiehuan09@...il.com, wangkefeng.wang@...wei.com,
 songmuchun@...edance.com, peterx@...hat.com, minchan@...nel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] mm/vmscan: avoid split PMD-mapped THP during
 shrink_folio_list()

On Wed, 24 Apr 2024 23:46:59 +0800 Lance Yang <ioworker0@...il.com> wrote:

> On Wed, Apr 24, 2024 at 12:15 PM Matthew Wilcox <willy@...radead.org> wrote:
> >
> > On Mon, Apr 22, 2024 at 01:52:13PM +0800, Lance Yang wrote:
> > > When the user no longer requires the pages, they would use
> > > madvise(MADV_FREE) to mark the pages as lazy free. IMO, they would not
> > > typically rewrite to the given range.
> > >
> > > At present, PMD-mapped THPs that are marked as lazyfree during
> > > shrink_folio_list() are unconditionally split, which may be unnecessary.
> > > If the THP is clean, its PMD is also clean, and there are no unexpected
> 
> "If the THP is clean, its PMD is also clean" can be confusing - sorry. It should
> be modified to "If the THP and its PMD are both marked as clean".

I made that changelog edit.