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From:   Hyeonggon Yoo <42.hyeyoo@gmail.com>
Date:   Tue, 5 Dec 2023 09:53:34 +0900
Message-ID: <CAB=+i9TVfzWk=anexu6ARPA21AC-uhjQjf4brZF0XDfVaWraWw@mail.gmail.com>
Subject: Re: [PATCH v2 3/3] mm/slub: correct the default value of
 slub_min_objects in doc
To:     sxwjean@me.com
Cc:     vbabka@suse.cz, cl@linux.com, linux-mm@kvack.org,
        penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com,
        roman.gushchin@linux.dev, corbet@lwn.net, keescook@chromium.org,
        arnd@arndb.de, akpm@linux-foundation.org,
        gregkh@linuxfoundation.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Xiongwei Song <xiongwei.song@windriver.com>
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On Sun, Dec 3, 2023 at 9:16=E2=80=AFAM <sxwjean@me.com> wrote:
>
> From: Xiongwei Song <xiongwei.song@windriver.com>
>
> There is no a value assigned to slub_min_objects by default, it always
> is 0 that is initialized by compiler if no assigned value by command line=
.
> min_objects is calculated based on processor numbers in calculate_order()=
.
> For more details, see commit 9b2cd506e5f2 ("slub: Calculate min_objects
> based on number of processors.")
>
> Signed-off-by: Xiongwei Song <xiongwei.song@windriver.com>

While slub_min_objects equals zero by default, 'min_objects' overrides it t=
o
4 * (fls(nr_cpus) + 1) when not set. so when slub_min_objects is not
set, it would be
equal to or higher than 4. I'm not sure this level of implementation
detail is worth documenting.

Also, I think patch 2 should update Documentation/mm/slub.rst too.
(slub_$param -> slab_param)

> ---
>  Documentation/mm/slub.rst | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/Documentation/mm/slub.rst b/Documentation/mm/slub.rst
> index be75971532f5..1f4399581449 100644
> --- a/Documentation/mm/slub.rst
> +++ b/Documentation/mm/slub.rst
> @@ -150,7 +150,7 @@ list_lock once in a while to deal with partial slabs.=
 That overhead is
>  governed by the order of the allocation for each slab. The allocations
>  can be influenced by kernel parameters:
>
> -.. slub_min_objects=3Dx          (default 4)
> +.. slub_min_objects=3Dx          (default 0)
>  .. slub_min_order=3Dx            (default 0)
>  .. slub_max_order=3Dx            (default 3 (PAGE_ALLOC_COSTLY_ORDER))
>
> --
> 2.34.1
>