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

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Message-ID: <aqdvjyzfk6vpespzcszfkmx522iy7hvddefcjgusrysglpdykt@uqedtngotzmy>
Date: Mon, 10 Nov 2025 08:47:57 -0800
From: Shakeel Butt <shakeel.butt@...ux.dev>
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, 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>, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 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 Mon, Nov 10, 2025 at 02:43:21PM +0900, Harry Yoo wrote:
> On Mon, Nov 10, 2025 at 12:30:06PM +0800, Qi Zheng wrote:
> > > Maybe we could make it safe against re-entrant IRQ handlers by using
> > > read-modify-write operations?
> > 
> > Isn't it because of the RMW operation that we need to use IRQ to
> > guarantee atomicity? Or have I misunderstood something?
> 
> I meant using atomic operations instead of disabling IRQs, like, by
> using this_cpu_add() or cmpxchg() instead.

We already have mod_node_page_state() which is safe from IRQs and is
optimized to not disable IRQs for archs with HAVE_CMPXCHG_LOCAL which
includes x86 and arm64.

Let me send the patch to cleanup the memcg code which uses
__mod_node_page_state.