linux-kernel - Re: [PATCH v1 04/26] mm: vmscan: refactor move_folios_to

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Message-ID: <20251107071832.Ty2LfTyY@linutronix.de>
Date: Fri, 7 Nov 2025 08:18:32 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Harry Yoo <harry.yoo@...cle.com>
Cc: Qi Zheng <qi.zheng@...ux.dev>, hannes@...xchg.org, hughd@...gle.com,
	mhocko@...e.com, roman.gushchin@...ux.dev, shakeel.butt@...ux.dev,
	muchun.song@...ux.dev, david@...hat.com, lorenzo.stoakes@...cle.com,
	ziy@...dia.com, imran.f.khan@...cle.com,
	kamalesh.babulal@...cle.com, axelrasmussen@...gle.com,
	yuanchu@...gle.com, weixugc@...gle.com, akpm@...ux-foundation.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org, Muchun Song <songmuchun@...edance.com>,
	Qi Zheng <zhengqi.arch@...edance.com>,
	Clark Williams <clrkwllms@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-rt-devel@...ts.linux.dev
Subject: Re: [PATCH v1 04/26] mm: vmscan: refactor move_folios_to_lru()

On 2025-11-07 14:11:27 [+0900], Harry Yoo wrote:
> > @@ -4735,14 +4734,15 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
> >  			set_mask_bits(&folio->flags.f, LRU_REFS_FLAGS, BIT(PG_active));
> >  	}
> >  
> > -	spin_lock_irq(&lruvec->lru_lock);
> > -
> > -	move_folios_to_lru(lruvec, &list);
> > +	move_folios_to_lru(&list);
> >  
> > +	local_irq_disable();
> >  	walk = current->reclaim_state->mm_walk;
> >  	if (walk && walk->batched) {
> >  		walk->lruvec = lruvec;
> > +		spin_lock(&lruvec->lru_lock);
> >  		reset_batch_size(walk);
> > +		spin_unlock(&lruvec->lru_lock);
> >  	}
> 
> Cc'ing RT folks as they may not want to disable IRQ on PREEMPT_RT.

Thank you, this is not going to work. The local_irq_disable() shouldn't
be used.

> IIRC there has been some effort in MM to reduce the scope of
> IRQ-disabled section in MM when PREEMPT_RT config was added to the
> mainline. spin_lock_irq() doesn't disable IRQ on PREEMPT_RT.
Exactly.

Sebastian