[RFC PATCH] mm: z3fold: rename CONFIG_Z3FOLD to CONFIG_Z3FOLD_DEPRECATED

[Nhat Pham]

On Fri, Jan 12, 2024 at 11:31 AM Yosry Ahmed <yosryahmed at google.com> wrote:
>
> The z3fold compressed pages allocator is not widely used, most users use
> zsmalloc. The only disadvantage of zsmalloc in comparison is the
> dependency on MMU, and zbud is a more common option for !MMU as it was
> the default zswap allocator for a long time.
>
> In hopes of having a single compressed pages allocator at some point,
> and following in the footsteps of SLAB, deprecate z3fold. Rename the
> user-visible option so that users with CONFIG_Z3FOLD=y get a new prompt
> with explanation during make oldconfig. Remove CONFIG_Z3FOLD=y from
> defconfigs.
>
> Existing users, if any, should voice their objections. Otherwise, we can
> remove z3fold in a few releases.
>
> Signed-off-by: Yosry Ahmed <yosryahmed at google.com>
> ---
> I have limited understanding of Kconfigs. I modelled this after commit
> eb07c4f39c3e ("mm/slab: rename CONFIG_SLAB to CONFIG_SLAB_DEPRECATED"),
> but one difference is that CONFIG_Z3FOLD is a tristate. I made
> CONFIG_Z3FOLD_DEPRECATED a boolean config, and CONFIG_Z3FOLD default y
> so that it is on by default if CONFIG_Z3FOLD_DEPRECATED is selected. I
> am not sure if that's the correct way to do this.
>
> ---
>  arch/loongarch/configs/loongson3_defconfig |  1 -
>  arch/powerpc/configs/ppc64_defconfig       |  1 -
>  mm/Kconfig                                 | 13 +++++++++++--
>  3 files changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/arch/loongarch/configs/loongson3_defconfig b/arch/loongarch/configs/loongson3_defconfig
> index 33795e4a5bd63..89b66b6c6a1d5 100644
> --- a/arch/loongarch/configs/loongson3_defconfig
> +++ b/arch/loongarch/configs/loongson3_defconfig
> @@ -85,7 +85,6 @@ CONFIG_ZPOOL=y
>  CONFIG_ZSWAP=y
>  CONFIG_ZSWAP_COMPRESSOR_DEFAULT_ZSTD=y
>  CONFIG_ZBUD=y
> -CONFIG_Z3FOLD=y
>  CONFIG_ZSMALLOC=m
>  # CONFIG_COMPAT_BRK is not set
>  CONFIG_MEMORY_HOTPLUG=y
> diff --git a/arch/powerpc/configs/ppc64_defconfig b/arch/powerpc/configs/ppc64_defconfig
> index 544a65fda77bc..d39284489aa26 100644
> --- a/arch/powerpc/configs/ppc64_defconfig
> +++ b/arch/powerpc/configs/ppc64_defconfig
> @@ -81,7 +81,6 @@ CONFIG_MODULE_SIG_SHA512=y
>  CONFIG_PARTITION_ADVANCED=y
>  CONFIG_BINFMT_MISC=m
>  CONFIG_ZSWAP=y
> -CONFIG_Z3FOLD=y
>  CONFIG_ZSMALLOC=y
>  # CONFIG_SLAB_MERGE_DEFAULT is not set
>  CONFIG_SLAB_FREELIST_RANDOM=y
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 1902cfe4cc4f5..bc6cc97c08349 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -193,15 +193,24 @@ config ZBUD
>           deterministic reclaim properties that make it preferable to a higher
>           density approach when reclaim will be used.
>
> -config Z3FOLD
> -       tristate "3:1 compression allocator (z3fold)"
> +config Z3FOLD_DEPRECATED
> +       bool "3:1 compression allocator (z3fold) (DEPRECATED)"
>         depends on ZSWAP
>         help
> +         Deprecated and scheduled for removal in a few cycles. If you have
> +         a good reason for using Z3FOLD rather than ZSMALLOC or ZBUD, please
> +         contact linux-mm at kvack.org and the zswap maintainers.
> +
>           A special purpose allocator for storing compressed pages.
>           It is designed to store up to three compressed pages per physical
>           page. It is a ZBUD derivative so the simplicity and determinism are
>           still there.
>
> +config Z3FOLD
> +       tristate
> +       default y
> +       depends on Z3FOLD_DEPRECATED
> +
>  config ZSMALLOC
>         tristate
>         prompt "N:1 compression allocator (zsmalloc)" if ZSWAP
> --
> 2.43.0.275.g3460e3d667-goog
>

FWIW:
Acked-by: Nhat Pham <nphamcs at gmail.com>