linux-kernel - Re: [PATCH v2] mm: skip folio_activate() for mlocked folios

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Message-Id: <20251015125911.0f0ebf87b278324667c4dfc5@linux-foundation.org>
Date: Wed, 15 Oct 2025 12:59:11 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Dmitry Ilvokhin <d@...okhin.com>
Cc: Shakeel Butt <shakeel.butt@...ux.dev>, Kemeng Shi
 <shikemeng@...weicloud.com>, Kairui Song <kasong@...cent.com>, Nhat Pham
 <nphamcs@...il.com>, Baoquan He <bhe@...hat.com>, Barry Song
 <baohua@...nel.org>, Chris Li <chrisl@...nel.org>, Axel Rasmussen
 <axelrasmussen@...gle.com>, Yuanchu Xie <yuanchu@...gle.com>, Wei Xu
 <weixugc@...gle.com>, Kiryl Shutsemau <kas@...nel.org>, Usama Arif
 <usamaarif642@...il.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 kernel-team@...a.com, hughd@...gle.com, yangge1116@....com,
 david@...hat.com
Subject: Re: [PATCH v2] mm: skip folio_activate() for mlocked folios

On Wed, 8 Oct 2025 18:06:07 +0000 Dmitry Ilvokhin <d@...okhin.com> wrote:

> > > +		 * They might be still in mlock_fbatch waiting to be processed
> > > +		 * and activating it here might interfere with
> > > +		 * mlock_folio_batch(). __mlock_folio() will fail
> > > +		 * folio_test_clear_lru() check and give up. It happens because
> > > +		 * __folio_batch_add_and_move() clears LRU flag, when adding
> > > +		 * folio to activate batch.
> > > +		 */
> > 
> > This makes sense as activating an mlocked folio should be a noop but I
> > am wondering why we are seeing this now. By this, I mean mlock()ed
> > memory being delayed to get to unevictable LRU. Also I remember Hugh
> > recently [1] removed the difference betwen mlock percpu cache and other
> > percpu caches of clearing LRU bit on entry. Does you repro work even
> > with Hugh's changes or without it?
> >
> 
> Thanks Shakeel for mentioning Hugh's patch, I was not aware of it.
> Indeed, I could not reproduce problem on top of Hugh's patch anymore,
> which totally make sense, because folio_test_clear_lru() is gone from
> __folio_batch_add_and_move().
> 
> Now I wonder does folio_test_mlocked() check still make sense in the
> current codebase?
> 
> > [1] https://lore.kernel.org/all/05905d7b-ed14-68b1-79d8-bdec30367eba@google.com/

So I take it that this patch ("mm: skip folio_activate() for mlocked
folios") is no longer needed?