Re: [PATCH v10 7/8] mm, folio_zero_user: support clearing page ranges

[Ankur Arora <ankur.a.arora@oracle.com>]

Andrew Morton <akpm@linux-foundation.org> writes:

> On Wed, 17 Dec 2025 00:48:50 -0800 Ankur Arora <ankur.a.arora@oracle.com> wrote:
>
>> > At 42GB/sec, 32MB will take less than a
>> > millisecond, yes?  I'm not aware of us really having any latency
>> > targets in these preemption modes, but 1 millisecond sounds pretty
>> > good.
>>
>> Agreed. The only complaint threshold I see is 100ms (default value of
>> sysctl_resched_latency_warn_ms) which is pretty far from ~1ms.
>>
>> And having a threshold of 32MB might benefit other applications since
>> we won't be discarding their cachelines in favour of filling up the
>> cache with zeroes.
>>
>> I think the only problem cases might be slow uarchs and workloads where
>> the memory bus is saturated which might dilate the preemption latency.
>>
>> And, even if the operation takes say ~20ms, that should still leave us
>> with a reasonably large margin.
>> (And, any latency senstive users are probably not running with
>> preempt=none/voluntary.)
>
> So I think you're saying that yes, we should increase the chunk size?

Yeah.

> If so, what's the timing on that?  It would be nice to do it in the
> current -rc cycle for testing reasons and so the changelogs can be
> updated to reflect the altered performance numbers.

I can send out an updated version of this patch later today. I think the
only real change is updating the constant and perf stats motivating
the chunk size value of 32MB.

Anything else you also think needs doing for this?

--
ankur