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From:   Hyeonggon Yoo <42.hyeyoo@gmail.com>
Date:   Tue, 21 Nov 2023 17:44:13 +0900
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Subject: Re: [PATCH 2/4] mm/slab: remove slab_nomrege and slab_merge
To:     sxwjean@me.com
Cc:     cl@linux.com, penberg@kernel.org, rientjes@google.com,
        iamjoonsoo.kim@lge.com, vbabka@suse.cz, roman.gushchin@linux.dev,
        corbet@lwn.net, linux-mm@kvack.org, linux-doc@vger.kernel.org,
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On Mon, Nov 20, 2023 at 6:12=E2=80=AFPM <sxwjean@me.com> wrote:
>
> From: Xiongwei Song <xiongwei.song@windriver.com>
>
> Since slab allocatoer has already been removed, so we should also remove
> the related parameters. And change the global flag from slab_nomerge
> to slub_nomerge.

No, kernel parameters should be changed only in a backward-compatible
way (if possible)

Before slab merging was supported in SLAB, only SLUB supported it.
After commit 423c929cbbec ("mm/slab_common: commonize slab merge logic"), u=
sing
slab_[no]merge parameters for CONFIG_SLUB builds became legal.

I think what the documentation says is "slab_[no]merge enables or
disables slab merging
and slub_[no]merge remain supported only for backward compatibility"

>
> Signed-off-by: Xiongwei Song <xiongwei.song@windriver.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 11 ++---------
>  mm/Kconfig                                      |  2 +-
>  mm/slab_common.c                                | 13 +++++--------
>  3 files changed, 8 insertions(+), 18 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentat=
ion/admin-guide/kernel-parameters.txt
> index c7709a11f8ce..afca9ff7c9f0 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5870,11 +5870,11 @@
>
>         slram=3D          [HW,MTD]
>
> -       slab_merge      [MM]
> +       slub_merge      [MM]
>                         Enable merging of slabs with similar size when th=
e
>                         kernel is built without CONFIG_SLAB_MERGE_DEFAULT=
.
>
> -       slab_nomerge    [MM]
> +       slub_nomerge    [MM]
>                         Disable merging of slabs with similar size. May b=
e
>                         necessary if there is some reason to distinguish
>                         allocs to different slabs, especially in hardened
> @@ -5915,13 +5915,6 @@
>                         lower than slub_max_order.
>                         For more information see Documentation/mm/slub.rs=
t.
>
> -       slub_merge      [MM, SLUB]
> -                       Same with slab_merge.
> -
> -       slub_nomerge    [MM, SLUB]
> -                       Same with slab_nomerge. This is supported for leg=
acy.
> -                       See slab_nomerge for more information.
> -
>         smart2=3D         [HW]
>                         Format: <io1>[,<io2>[,...,<io8>]]