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

Qi Zheng
2025-11-11T03:25:02Z

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.

>