linux-kernel - Re: [RFC PATCH v2 3/3] mm: mlock: update mlock_pte

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Date:   Sun, 16 Jul 2023 18:35:09 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     "Yin, Fengwei" <fengwei.yin@...el.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, willy@...radead.org, david@...hat.com,
        ryan.roberts@....com, shy828301@...il.com
Subject: Re: [RFC PATCH v2 3/3] mm: mlock: update mlock_pte_range to handle
 large folio

On Sun, Jul 16, 2023 at 6:00 PM Yin, Fengwei <fengwei.yin@...el.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 always.

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