linux-kernel - Re: [RFC PATCH 00/11] Add a percpu subsection for hot data

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Message-ID: <CAHk-=wjSoFLsyU4Hz6BzoRGTWh_HqEo2fm2T8jvvEnAHB_i5Ag@mail.gmail.com>
Date: Sun, 23 Feb 2025 10:00:05 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: Brian Gerst <brgerst@...il.com>, linux-kernel@...r.kernel.org, x86@...nel.org, 
	"H . Peter Anvin" <hpa@...or.com>, Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, 
	Ard Biesheuvel <ardb@...nel.org>, Uros Bizjak <ubizjak@...il.com>, Andy Lutomirski <luto@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 00/11] Add a percpu subsection for hot data

On Sun, 23 Feb 2025 at 01:37, Ingo Molnar <mingo@...nel.org> wrote:
>
> This can also be a drawback if it's abused by random driver code - so I
> think it should at minimum be documented to be used by core & arch
> code. Maybe add a build #error too if it's defined in modular code?

Yes, please.

Everybody always thinks that *their* code is the most important code,
so making it easy for random filesystems or drivers to just say "this
is my hot piece of data" needs to be avoided.

That is also an argument for having the final size be asserted to be
smaller than one cacheline.

Because I do think that the patches look fine, but it's too much of an
invitation for random developers to go "Oh, *MY* code deserves a hot
marker".

           Linus