Re: [PATCH v7 3/4] mm: huge_memory: refactor enabled_store() with set_global_enabled_mode()

[Lorenzo Stoakes (Oracle)]

On Tue, Mar 17, 2026 at 08:33:58AM -0700, Breno Leitao wrote:
> Refactor enabled_store() to use a new set_global_enabled_mode() helper.
> Introduce a separate enum global_enabled_mode and
> global_enabled_mode_strings[], mirroring the anon_enabled_mode
> pattern from the previous commit.
>
> A separate enum is necessary because the global THP setting does
> not support "inherit", only "always", "madvise", and "never".
> Reusing anon_enabled_mode would leave a NULL gap in the string
> array, causing sysfs_match_string() to stop early and fail to
> match entries after the gap.
>
> The helper uses the same loop pattern as set_anon_enabled_mode(),
> iterating over an array of flag bit positions and using
> test_and_set_bit()/test_and_clear_bit() to track whether the state
> actually changed.
>
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@xxxxxxxxxx>
> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Reviewed-by: Wei Yang <richard.weiyang@xxxxxxxxx>
> Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
> ---
>  mm/huge_memory.c | 63 ++++++++++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 48 insertions(+), 15 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index f6af90e6cf05d..b95fde5843399 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -330,30 +330,63 @@ static const char * const anon_enabled_mode_strings[] = {
>  	[ANON_ENABLED_NEVER]	= "never",
>  };
>
> +enum global_enabled_mode {
> +	GLOBAL_ENABLED_ALWAYS	= 0,
> +	GLOBAL_ENABLED_MADVISE	= 1,
> +	GLOBAL_ENABLED_NEVER	= 2,
> +};
> +
> +static const char * const global_enabled_mode_strings[] = {
> +	[GLOBAL_ENABLED_ALWAYS]		= "always",
> +	[GLOBAL_ENABLED_MADVISE]	= "madvise",
> +	[GLOBAL_ENABLED_NEVER]		= "never",
> +};
> +
> +static bool set_global_enabled_mode(enum global_enabled_mode mode)
> +{
> +	static const unsigned long thp_flags[] = {
> +		TRANSPARENT_HUGEPAGE_FLAG,
> +		TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
> +	};
> +	enum global_enabled_mode m;
> +	bool changed = false;
> +
> +	for (m = 0; m < ARRAY_SIZE(thp_flags); m++) {
> +		if (m == mode)
> +			changed |= !test_and_set_bit(thp_flags[m],
> +						     &transparent_hugepage_flags);
> +		else
> +			changed |= test_and_clear_bit(thp_flags[m],
> +						      &transparent_hugepage_flags);

LGTM!

> +	}
> +
> +	return changed;
> +}
> +
>  static ssize_t enabled_store(struct kobject *kobj,
>  			     struct kobj_attribute *attr,
>  			     const char *buf, size_t count)
>  {
> -	ssize_t ret = count;
> +	int mode;
>
> -	if (sysfs_streq(buf, "always")) {
> -		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
> -		set_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
> -	} else if (sysfs_streq(buf, "madvise")) {
> -		clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
> -		set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
> -	} else if (sysfs_streq(buf, "never")) {
> -		clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
> -		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
> -	} else
> -		ret = -EINVAL;
> +	mode = sysfs_match_string(global_enabled_mode_strings, buf);
> +	if (mode < 0)
> +		return -EINVAL;
>
> -	if (ret > 0) {
> +	if (set_global_enabled_mode(mode)) {
>  		int err = start_stop_khugepaged();
> +
>  		if (err)
> -			ret = err;
> +			return err;
> +	} else {
> +		/*
> +		 * Recalculate watermarks even when the mode didn't
> +		 * change, as the previous code always called
> +		 * start_stop_khugepaged() which does this internally.
> +		 */
> +		set_recommended_min_free_kbytes();
>  	}
> -	return ret;
> +	return count;
>  }
>
>  static struct kobj_attribute enabled_attr = __ATTR_RW(enabled);
>
> --
> 2.52.0
>