linux-kernel - Re: Selecting MMU page size for an architecture

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Message-ID: <871r0x45fd.fsf@osv.gnss.ru>
Date:   Mon, 24 Jan 2022 16:41:26 +0300
From:   Sergey Organov <sorganov@...il.com>
To:     Jon Masters <jcm@...masters.org>
Cc:     lkml <linux-kernel@...r.kernel.org>
Subject: Re: Selecting MMU page size for an architecture

Hi Jon,

Jon Masters <jcm@...masters.org> writes:

> Hey Sergey,
>
> On Thu, Dec 23, 2021 at 8:15 AM Sergey Organov <sorganov@...il.com> wrote:
>
>> We are building custom CPU and have an option to choose either 4K or 16K
>> MMU minimum page size that will then be fixed in the hardware. For
>> reasons unrelated to the Linux kernel we'd prefer 16K, but I have some
>> doubts.
>>
>> What pros and cons for kernel and user-space operation 16K pages will
>> have over more usual 4K pages? Anything we should worry about?
>
> If you want maximum compatibility with existing source written for
> industry at large (e.g. x86/Arm) and even the assumptions in other
> devices (and their firmware) you might connect (PCI, or even on-SoC)
> then you'll want to go with 4K. However, if I were designing a brand
> new architecture today and didn't care about legacy, I would
> definitely consider following Apple into 16K.

I don't think we will have issues with device drivers because of this,
but even if so, I believe we'll be able to fix that, so I get your
advice as +1 in favor of 16K pages.

Thanks for sharing!

-- Sergey Organov