linux-kernel - Re: [PATCH v3 4/4] x86/folio_zero

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Message-ID: <2c74c021-f985-4cfc-8369-57fc525a8070@amd.com>
Date: Tue, 22 Apr 2025 12:06:11 +0530
From: Raghavendra K T <raghavendra.kt@....com>
To: Ingo Molnar <mingo@...nel.org>, Ankur Arora <ankur.a.arora@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
 torvalds@...ux-foundation.org, akpm@...ux-foundation.org, bp@...en8.de,
 dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
 luto@...nel.org, peterz@...radead.org, paulmck@...nel.org,
 rostedt@...dmis.org, tglx@...utronix.de, willy@...radead.org,
 jon.grimm@....com, bharata@....com, boris.ostrovsky@...cle.com,
 konrad.wilk@...cle.com
Subject: Re: [PATCH v3 4/4] x86/folio_zero_user: multi-page clearing



On 4/14/2025 12:35 PM, Ingo Molnar wrote:
> 
> * Ankur Arora <ankur.a.arora@...cle.com> wrote:

[...]

>> Performance for preempt=none|voluntary remains unchanged.
> 
> CONFIG_PREEMPT_VOLUNTARY=y is the default on a number of major
> distributions, such as Ubuntu, and a lot of enterprise distro kernels -
> and this patch does nothing for them, for no good reason.
> 
> So could you please provide a sensible size granularity cutoff of 16MB
> or so on non-preemptive kernels, instead of this weird build-time
> all-or-nothing binary cutoff based on preemption modes?
> 

Agree with Ingo here. We are too harsh on none and voluntary with this
limit. At least 512KB size?

I will try to see if I can get numbers for different sizes that does not 
interfere much with other workloads' perf. (in none/voluntary mode).

- Raghu