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

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Message-ID: <aO__XXIJShKz3-Tn@shell.ilvokhin.com>
Date: Wed, 15 Oct 2025 20:09:01 +0000
From: Dmitry Ilvokhin <d@...okhin.com>
To: Andrew Morton <akpm@...ux-foundation.org>
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, Oct 15, 2025 at 12:59:11PM -0700, Andrew Morton wrote:
> 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?

Yes, this is my understanding as well. Hugh's patch addressed initial
problem and this patch is no longer needed.