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From:   Yu Zhao <yuzhao@google.com>
Date:   Sun, 16 Jul 2023 18:35:09 -0600
Message-ID: <CAOUHufZHyEvU-c2O6B6stM_QVMxc22zV4Szn52myYqjdZvptUA@mail.gmail.com>
Subject: Re: [RFC PATCH v2 3/3] mm: mlock: update mlock_pte_range to handle
 large folio
To:     "Yin, Fengwei" <fengwei.yin@intel.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        akpm@linux-foundation.org, willy@infradead.org, david@redhat.com,
        ryan.roberts@arm.com, shy828301@gmail.com
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On Sun, Jul 16, 2023 at 6:00=E2=80=AFPM Yin, Fengwei <fengwei.yin@intel.com=
> wrote:
>
> On 7/15/2023 2:06 PM, Yu Zhao wrote:
> > There is a problem here that I didn't have the time to elaborate: we
> > can't mlock() a folio that is within the range but not fully mapped
> > because this folio can be on the deferred split queue. When the split
> > happens, those unmapped folios (not mapped by this vma but are mapped
> > into other vmas) will be stranded on the unevictable lru.
>
> This should be fine unless I missed something. During large folio split,
> the unmap_folio() will be migrate(anon)/unmap(file) folio. Folio will be
> munlocked in unmap_folio(). So the head/tail pages will be evictable alwa=
ys.

It's close but not entirely accurate: munlock can fail on isolated folios.