Re: [PATCH v3] mm/zsmalloc: remove CONFIG_ZSMALLOC_STAT

[Dongliang Mu <dzm91@hust.edu.cn>]

On 11/11/26 8:41 PM, Xueyuan Chen wrote:
> CONFIG_ZSMALLOC_STAT only controls the debugfs interface. The class
> counters are updated regardless of this option.
>
> Remove the CONFIG_ZSMALLOC_STAT guards and rely on the debugfs API
> stubs when CONFIG_DEBUG_FS=n. Skip statistics setup silently when
> debugfs is unavailable.
>
> Remove the Kconfig entry and replace the existing CONFIG_ZSMALLOC_STAT
> settings with CONFIG_DEBUG_FS=y. Update the English and Chinese
> documentation to match, and clarify the pool name in the debugfs path.
>
> Suggested-by: Nhat Pham <nphamcs@gmail.com>
> Reviewed-by: Nhat Pham <nphamcs@gmail.com>
> Signed-off-by: Xueyuan Chen <xueyuan.chen21@gmail.com>

|The documentation changes look good to me. Acked-by: Dongliang Mu 
<dzm91@hust.edu.cn> # Documentation|

> ---
> Drop CONFIG_ZSMALLOC_STAT instead of making the counters conditional. The
> option only controls the debugfs interface, while the class counters are
> updated unconditionally. Removing it simplifies the code.
>
> Following Nhat's suggestion, remove CONFIG_ZSMALLOC_STAT and rely on
> the existing debugfs API stubs when CONFIG_DEBUG_FS=n.
> ---
> Changes in v3:
> - Squash the three patches into one (Nhat, Sergey).
> - Add Nhat's Reviewed-by.
> - Update the documentation wording.
> - Link to v2: https://patch.msgid.link/20261109-zsmalloc_stat-v2-0-caee41684aba@gmail.com
>
> Changes in v2:
> - Drop CONFIG_ZSMALLOC_STAT instead of making the counters conditional.
> - Update configuration files and documentation.
> - Link to v1: https://patch.msgid.link/20261106-zsmalloc_stat-v1-1-b574f4714adf@gmail.com
> ---
>   Documentation/mm/zsmalloc.rst                    |  4 +--
>   Documentation/translations/zh_CN/mm/zsmalloc.rst |  2 +-
>   arch/s390/configs/debug_defconfig                |  2 +-
>   arch/s390/configs/defconfig                      |  2 +-
>   drivers/gpu/drm/ci/arm.config                    |  2 +-
>   drivers/gpu/drm/ci/arm64.config                  |  2 +-
>   drivers/gpu/drm/ci/x86_64.config                 |  2 +-
>   mm/Kconfig                                       |  9 -------
>   mm/zsmalloc.c                                    | 33 ++----------------------
>   9 files changed, 10 insertions(+), 48 deletions(-)
>
> diff --git a/Documentation/mm/zsmalloc.rst b/Documentation/mm/zsmalloc.rst
> index d2bbecd78e14..4c0786378dc3 100644
> --- a/Documentation/mm/zsmalloc.rst
> +++ b/Documentation/mm/zsmalloc.rst
> @@ -33,8 +33,8 @@ proper handle-based APIs.
>   stat
>   ====
>   
> -With CONFIG_ZSMALLOC_STAT, we could see zsmalloc internal information via
> -``/sys/kernel/debug/zsmalloc/<user name>``. Here is a sample of stat output::
> +With CONFIG_DEBUG_FS, we could see zsmalloc internal information via
> +``/sys/kernel/debug/zsmalloc/<pool-name>``. Here is a sample of stat output::
>   
>    # cat /sys/kernel/debug/zsmalloc/zram0/classes
>   
> diff --git a/Documentation/translations/zh_CN/mm/zsmalloc.rst b/Documentation/translations/zh_CN/mm/zsmalloc.rst
> index 4c8c9b1006a9..b555a07ac871 100644
> --- a/Documentation/translations/zh_CN/mm/zsmalloc.rst
> +++ b/Documentation/translations/zh_CN/mm/zsmalloc.rst
> @@ -32,7 +32,7 @@ zs_unmap_object()解除映射。
>   stat
>   ====
>   
> -通过CONFIG_ZSMALLOC_STAT，我们可以通过 ``/sys/kernel/debug/zsmalloc/<user name>``
> +启用CONFIG_DEBUG_FS，我们可以通过 ``/sys/kernel/debug/zsmalloc/<pool-name>``
>   看到zsmalloc内部信息。下面是一个统计输出的例子。::
>   
>    # cat /sys/kernel/debug/zsmalloc/zram0/classes
> diff --git a/arch/s390/configs/debug_defconfig b/arch/s390/configs/debug_defconfig
> index d44674b63715..83193ef8efb9 100644
> --- a/arch/s390/configs/debug_defconfig
> +++ b/arch/s390/configs/debug_defconfig
> @@ -100,7 +100,7 @@ CONFIG_UNIXWARE_DISKLABEL=y
>   CONFIG_IOSCHED_BFQ=y
>   CONFIG_BINFMT_MISC=m
>   CONFIG_ZSWAP=y
> -CONFIG_ZSMALLOC_STAT=y
> +CONFIG_DEBUG_FS=y
>   CONFIG_SLAB_BUCKETS=y
>   CONFIG_SLUB_STATS=y
>   # CONFIG_COMPAT_BRK is not set
> diff --git a/arch/s390/configs/defconfig b/arch/s390/configs/defconfig
> index e00e252d4694..694a309377d5 100644
> --- a/arch/s390/configs/defconfig
> +++ b/arch/s390/configs/defconfig
> @@ -94,7 +94,7 @@ CONFIG_UNIXWARE_DISKLABEL=y
>   CONFIG_IOSCHED_BFQ=y
>   CONFIG_BINFMT_MISC=m
>   CONFIG_ZSWAP=y
> -CONFIG_ZSMALLOC_STAT=y
> +CONFIG_DEBUG_FS=y
>   CONFIG_SLAB_BUCKETS=y
>   # CONFIG_COMPAT_BRK is not set
>   CONFIG_MEMORY_HOTPLUG=y
> diff --git a/drivers/gpu/drm/ci/arm.config b/drivers/gpu/drm/ci/arm.config
> index d7c51670da2f..fc0a8a4bfb18 100644
> --- a/drivers/gpu/drm/ci/arm.config
> +++ b/drivers/gpu/drm/ci/arm.config
> @@ -5,7 +5,7 @@ CONFIG_CRYPTO_ZSTD=y
>   CONFIG_ZRAM_MEMORY_TRACKING=y
>   CONFIG_ZRAM_WRITEBACK=y
>   CONFIG_ZRAM=y
> -CONFIG_ZSMALLOC_STAT=y
> +CONFIG_DEBUG_FS=y
>   
>   # abootimg with a 'dummy' rootfs fails with root=/dev/nfs
>   CONFIG_BLK_DEV_INITRD=n
> diff --git a/drivers/gpu/drm/ci/arm64.config b/drivers/gpu/drm/ci/arm64.config
> index c46125c1f80f..10b01b55a66d 100644
> --- a/drivers/gpu/drm/ci/arm64.config
> +++ b/drivers/gpu/drm/ci/arm64.config
> @@ -5,7 +5,7 @@ CONFIG_CRYPTO_ZSTD=y
>   CONFIG_ZRAM_MEMORY_TRACKING=y
>   CONFIG_ZRAM_WRITEBACK=y
>   CONFIG_ZRAM=y
> -CONFIG_ZSMALLOC_STAT=y
> +CONFIG_DEBUG_FS=y
>   
>   # abootimg with a 'dummy' rootfs fails with root=/dev/nfs
>   CONFIG_BLK_DEV_INITRD=n
> diff --git a/drivers/gpu/drm/ci/x86_64.config b/drivers/gpu/drm/ci/x86_64.config
> index 7ac98a78691e..8225b806dad8 100644
> --- a/drivers/gpu/drm/ci/x86_64.config
> +++ b/drivers/gpu/drm/ci/x86_64.config
> @@ -5,7 +5,7 @@ CONFIG_CRYPTO_ZSTD=y
>   CONFIG_ZRAM_MEMORY_TRACKING=y
>   CONFIG_ZRAM_WRITEBACK=y
>   CONFIG_ZRAM=y
> -CONFIG_ZSMALLOC_STAT=y
> +CONFIG_DEBUG_FS=y
>   
>   CONFIG_PWM=y
>   CONFIG_PM_DEVFREQ=y
> diff --git a/mm/Kconfig b/mm/Kconfig
> index afff1b25b543..4a77cda7f1d7 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -130,15 +130,6 @@ menu "Zsmalloc allocator options"
>   
>   comment "Zsmalloc is a common backend allocator for zswap & zram"
>   
> -config ZSMALLOC_STAT
> -	bool "Export zsmalloc statistics"
> -	select DEBUG_FS
> -	help
> -	  This option enables code in the zsmalloc to collect various
> -	  statistics about what's happening in zsmalloc and exports that
> -	  information to userspace via debugfs.
> -	  If unsure, say N.
> -
>   config ZSMALLOC_CHAIN_SIZE
>   	int "Maximum number of physical pages per-zspage"
>   	default 8
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 7ef80e0da626..104ccf3aa170 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -222,9 +222,7 @@ struct zs_size_stat {
>   	unsigned long objs[NR_CLASS_STAT_TYPES];
>   };
>   
> -#ifdef CONFIG_ZSMALLOC_STAT
>   static struct dentry *zs_stat_root;
> -#endif
>   
>   static size_t huge_class_size;
>   
> @@ -279,9 +277,7 @@ struct zs_pool {
>   	/* Compact classes */
>   	struct shrinker *shrinker;
>   
> -#ifdef CONFIG_ZSMALLOC_STAT
>   	struct dentry *stat_dentry;
> -#endif
>   #ifdef CONFIG_COMPACTION
>   	struct work_struct free_work;
>   #endif
> @@ -565,14 +561,10 @@ static inline unsigned long class_stat_read(struct size_class *class, int type)
>   	return class->stats.objs[type];
>   }
>   
> -#ifdef CONFIG_ZSMALLOC_STAT
> -
>   static void __init zs_stat_init(void)
>   {
> -	if (!debugfs_initialized()) {
> -		pr_warn("debugfs not available, stat dir not created\n");
> +	if (!debugfs_initialized())
>   		return;
> -	}
>   
>   	zs_stat_root = debugfs_create_dir("zsmalloc", NULL);
>   }
> @@ -650,10 +642,8 @@ DEFINE_SHOW_ATTRIBUTE(zs_stats_size);
>   
>   static void zs_pool_stat_create(struct zs_pool *pool, const char *name)
>   {
> -	if (!zs_stat_root) {
> -		pr_warn("no root stat dir, not creating <%s> stat dir\n", name);
> +	if (IS_ERR_OR_NULL(zs_stat_root))
>   		return;
> -	}
>   
>   	pool->stat_dentry = debugfs_create_dir(name, zs_stat_root);
>   
> @@ -666,25 +656,6 @@ static void zs_pool_stat_destroy(struct zs_pool *pool)
>   	debugfs_remove_recursive(pool->stat_dentry);
>   }
>   
> -#else /* CONFIG_ZSMALLOC_STAT */
> -static void __init zs_stat_init(void)
> -{
> -}
> -
> -static void __exit zs_stat_exit(void)
> -{
> -}
> -
> -static inline void zs_pool_stat_create(struct zs_pool *pool, const char *name)
> -{
> -}
> -
> -static inline void zs_pool_stat_destroy(struct zs_pool *pool)
> -{
> -}
> -#endif
> -
> -
>   /*
>    * For each size class, zspages are divided into different groups
>    * depending on their usage ratio. This function returns fullness
>
> ---
> base-commit: fa4ad798f6f681031775266044ba1b0cf3c670bd
>
> --
> Best regards,
> Xueyuan