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

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Message-ID: <87345851kg.fsf@oracle.com>
Date: Wed, 17 Dec 2025 11:51:43 -0800
From: Ankur Arora <ankur.a.arora@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Ankur Arora <ankur.a.arora@...cle.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org, david@...nel.org, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        mjguzik@...il.com, luto@...nel.org, peterz@...radead.org,
        tglx@...utronix.de, willy@...radead.org, raghavendra.kt@....com,
        chleroy@...nel.org, ioworker0@...il.com, boris.ostrovsky@...cle.com,
        konrad.wilk@...cle.com
Subject: Re: [PATCH v10 7/8] mm, folio_zero_user: support clearing page ranges


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

> On Wed, 17 Dec 2025 00:48:50 -0800 Ankur Arora <ankur.a.arora@...cle.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