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

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Message-Id: <20251217105426.5f03b5e8abd2e50faee9f49f@linux-foundation.org>
Date: Wed, 17 Dec 2025 10:54:26 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Ankur Arora <ankur.a.arora@...cle.com>
Cc: 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

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?

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.