linux-kernel - Re: [patch 00/13] preempt: Make preempt count unconditional

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Date:   Tue, 15 Sep 2020 10:29:50 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Ard Biesheuvel <ardb@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
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Subject: Re: [patch 00/13] preempt: Make preempt count unconditional

On Tue, Sep 15, 2020 at 12:24 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> Alternatively we just make highmem a bit more expensive by making these
> maps preemptible. RT is doing this for a long time and it's not that
> horrible.

Ack.

In fact, I've wanted to start just removing kmap support entirely. At
some point it's not so much about "I have an old machine that wants
HIGHMEM" but about "I have an old CPU, and I'll just run an old
kernel".

It's not that 32-bit is irrelevant, it's that 32-bit with large
amounts of memory is irrelevant.

Last time this was discussed, iirc the main issue was some
questionable old ARM chips that were still very common in embedded
environments, even with large memory.

But we could definitely start de-emphasizing HIGHMEM.

                     Linus