Re: [PATCH v1 04/26] mm: vmscan: refactor move_folios_to_lru()

[Qi Zheng]

On 11/11/25 11:17 AM, Shakeel Butt wrote:
> On Tue, Nov 11, 2025 at 11:04:09AM +0800, Qi Zheng wrote:
> > On 11/11/25 12:47 AM, Shakeel Butt wrote:
> > > 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.
> >
> > However, in the !CONFIG_HAVE_CMPXCHG_LOCAL case, mod_node_page_state()
> > still calls local_irq_save(). Is this feasible in the PREEMPT_RT kernel?
>
> Yes we can disable irqs on PREEMPT_RT but it is usually frown upon and
> it is usually requested to do so only for short window. However if

Got it.

> someone running PREEMPT_RT on an arch without HAVE_CMPXCHG_LOCAL and has
> issues with mod_node_page_state() then they can solve it then. I don't
> think we need to fix that now.

OK.

>