linux-kernel - Re: [PATCH] Documentation/features: mark BATCHED_UNMAP_TLB

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Message-ID: <87a6r42pjy.fsf@meer.lwn.net>
Date:   Mon, 15 Mar 2021 13:18:57 -0600
From:   Jonathan Corbet <corbet@....net>
To:     Barry Song <song.bao.hua@...ilicon.com>, linux-doc@...r.kernel.org,
        akpm@...ux-foundation.org, linux-mm@...ck.org
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linuxarm@...neuler.org, Barry Song <song.bao.hua@...ilicon.com>,
        Mel Gorman <mgorman@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH] Documentation/features: mark BATCHED_UNMAP_TLB_FLUSH
 doesn't apply to ARM64

Barry Song <song.bao.hua@...ilicon.com> writes:

> BATCHED_UNMAP_TLB_FLUSH is used on x86 to do batched tlb shootdown by
> sending one IPI to TLB flush all entries after unmapping pages rather
> than sending an IPI to flush each individual entry.
> On arm64, tlb shootdown is done by hardware. Flush instructions are
> innershareable. The local flushes are limited to the boot (1 per CPU)
> and when a task is getting a new ASID.
> So marking this feature as "TODO" is not proper. ".." isn't good as
> well. So this patch adds a "N/A" for this kind of features which are
> not needed on some architectures.
>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Signed-off-by: Barry Song <song.bao.hua@...ilicon.com>
> ---
>  Documentation/features/arch-support.txt        | 1 +
>  Documentation/features/vm/TLB/arch-support.txt | 2 +-
>  2 files changed, 2 insertions(+), 1 deletion(-)

This had a conflict with the c6x removal, but I fixed that up and
(finally) applied it, thanks.

jon