linux-kernel - Re: [PATCH v3 11/34] mips: mm: Add p?d

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Date:   Thu, 28 Feb 2019 02:15:28 +0000
From:   Paul Burton <paul.burton@...s.com>
To:     Steven Price <steven.price@....com>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andy Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        James Morse <james.morse@....com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        "x86@...nel.org" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Rutland <Mark.Rutland@....com>,
        "Liang, Kan" <kan.liang@...ux.intel.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>
Subject: Re: [PATCH v3 11/34] mips: mm: Add p?d_large() definitions

Hi Steven,

On Wed, Feb 27, 2019 at 05:05:45PM +0000, Steven Price wrote:
> For mips, we don't support large pages on 32 bit so add stubs returning 0.

So far so good :)

> For 64 bit look for _PAGE_HUGE flag being set. This means exposing the
> flag when !CONFIG_MIPS_HUGE_TLB_SUPPORT.

Here I have to ask why? We could just return 0 like the mips32 case when
CONFIG_MIPS_HUGE_TLB_SUPPORT=n, let the compiler optimize the whole
thing out and avoid redundant work at runtime.

This could be unified too in asm/pgtable.h - checking for
CONFIG_MIPS_HUGE_TLB_SUPPORT should be sufficient to cover the mips32
case along with the subset of mips64 configurations without huge pages.

Thanks,
    Paul