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In-Reply-To: <a2b2528f6d96fbc6a0c68f16e7212f80f3ef1505.1638825394.git.andreyknvl@google.com>
From:   Andrey Konovalov <andreyknvl@gmail.com>
Date:   Tue, 7 Dec 2021 18:33:09 +0100
Message-ID: <CA+fCnZfQr191GvWf+T2=HB3bLK2-sE4DgHSJcXsahM5BN_nPPg@mail.gmail.com>
Subject: Re: [PATCH v2 07/34] mm: clarify __GFP_ZEROTAGS comment
To:     Peter Collingbourne <pcc@google.com>
Cc:     Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Evgenii Stepanov <eugenis@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        andrey.konovalov@linux.dev
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On Mon, Dec 6, 2021 at 10:44 PM <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@google.com>
>
> __GFP_ZEROTAGS is intended as an optimization: if memory is zeroed during
> allocation, it's possible to set memory tags at the same time with little
> performance impact.
>
> Clarify this intention of __GFP_ZEROTAGS in the comment.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
>  include/linux/gfp.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index b976c4177299..dddd7597689f 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -232,8 +232,8 @@ struct vm_area_struct;
>   *
>   * %__GFP_ZERO returns a zeroed page on success.
>   *
> - * %__GFP_ZEROTAGS returns a page with zeroed memory tags on success, if
> - * __GFP_ZERO is set.
> + * %__GFP_ZEROTAGS zeroes memory tags at allocation time if the memory itself
> + * is being zeroed (either via __GFP_ZERO or via init_on_alloc).
>   *
>   * %__GFP_SKIP_KASAN_POISON returns a page which does not need to be poisoned
>   * on deallocation. Typically used for userspace pages. Currently only has an
> --
> 2.25.1
>

Hi Peter,

Could you check whether I correctly understood the intention of
__GFP_ZEROTAGS and give your ack on this patch and the next one?

Thanks!