linux-kernel - Re: [PATCH v3 05/10] x86: remove HIGHMEM64G support

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Message-ID: <CAHk-=wjFb7jeWXB2wovPeHqZ7XaxfiCbb+Vgk9FeGO2pcY78zA@mail.gmail.com>
Date: Thu, 27 Feb 2025 08:51:59 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: Arnd Bergmann <arnd@...nel.org>, linux-kernel@...r.kernel.org, x86@...nel.org, 
	Arnd Bergmann <arnd@...db.de>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Andy Shevchenko <andy@...nel.org>, Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v3 05/10] x86: remove HIGHMEM64G support

On Thu, 27 Feb 2025 at 07:41, H. Peter Anvin <hpa@...or.com> wrote:
>
> One of the generations of kernel.org ran on a dual socket system with
> 6 GiB RAM. It was a mess; basically it achieved less than 50% memory
> utilization because of highmem.

I'll be very very happy when HIGHMEM is gone completely, but yes,
HIGHMEM64G was particularly painful.

It was definitely used, and it worked better under some loads than
others (large user footprints with lots of anonymous memory and little
kernel side memory pressure), but it was not great in general.

I suspect that absolutely everybody who ever used it switched to
64-bit as soon as humanly possible and nobody has likely actively used
it for a *long* time.

Good riddance,

            Linus