linux-kernel - Re: [PATCH v10 05/12] mm: HUGE

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Date:   Mon, 25 Jan 2021 09:40:53 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Nicholas Piggin <npiggin@...il.com>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, Zefan Li <lizefan@...wei.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Christoph Hellwig <hch@...radead.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Ding Tianhong <dingtianhong@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v10 05/12] mm: HUGE_VMAP arch support cleanup



Le 24/01/2021 à 09:22, Nicholas Piggin a écrit :
> This changes the awkward approach where architectures provide init
> functions to determine which levels they can provide large mappings for,
> to one where the arch is queried for each call.
> 
> This removes code and indirection, and allows constant-folding of dead
> code for unsupported levels.

It looks like this is only the case when CONFIG_HAVE_ARCH_HUGE_VMAP is not defined.

When it is defined, for exemple on powerpc you defined arch_vmap_p4d_supported() as a regular 
function in arch/powerpc/mm/book3s64/radix_pgtable.c, so allthough it returns always false, it won't 
constant fold dead code.

> 
> This also adds a prot argument to the arch query. This is unused
> currently but could help with some architectures (e.g., some powerpc
> processors can't map uncacheable memory with large pages).
> 
> Cc: linuxppc-dev@...ts.ozlabs.org
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: x86@...nel.org
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Acked-by: Catalin Marinas <catalin.marinas@....com> [arm64]
> Signed-off-by: Nicholas Piggin <npiggin@...il.com>
> ---
>   arch/arm64/include/asm/vmalloc.h         |  8 +++
>   arch/arm64/mm/mmu.c                      | 10 +--
>   arch/powerpc/include/asm/vmalloc.h       |  8 +++
>   arch/powerpc/mm/book3s64/radix_pgtable.c |  8 +--
>   arch/x86/include/asm/vmalloc.h           |  7 ++
>   arch/x86/mm/ioremap.c                    | 12 ++--
>   include/linux/io.h                       |  9 ---
>   include/linux/vmalloc.h                  |  6 ++
>   init/main.c                              |  1 -
>   mm/ioremap.c                             | 88 +++++++++---------------
>   10 files changed, 79 insertions(+), 78 deletions(-)
> 

Christophe