Re: [PATCH v3 1/2] mm: shmem: refactor thpsize_shmem_enabled_store() with sysfs_match_string()

[Lorenzo Stoakes <ljs@kernel.org>]

On Mon, May 18, 2026 at 12:32:37PM +0000, ranxiaokai627@163.com wrote:
> From: Ran Xiaokai <ran.xiaokai@zte.com.cn>
>
> Inspired by commit 82d9ff648c6c ("mm: huge_memory: refactor
> anon_enabled_store() with set_anon_enabled_mode()"), refactor
> thpsize_shmem_enabled_store() using sysfs_match_string().
> This eliminates the duplicated spin_lock/unlock(), set/clear_bit(),
> calls across all branches, reducing code duplication.
>
> Behavioral change:
> Call start_stop_khugepaged() only when the mode actually changes.
> If unchanged, call set_recommended_min_free_kbytes() to preserve
> legacy watermark behavior. This avoids unnecessary khugepaged restarts.
>
> Tested with selftests ./run_kselftest.sh -t mm:ksft_thp.sh,
> all test cases passed.
>
> Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>

Your From: and Signed-off-by: differs. As per my mail to the 2/2 this violates
kernel process rules. Please either update the signed-off-by to your @163.com
address or resend from your zte.com.cn address.

Logic generally looks good, but you need to fix your From/Signed-off-by and the
rename suggested below would be good.

Thanks, Lorenzo

> ---
>  mm/shmem.c | 107 ++++++++++++++++++++++++++++++-----------------------
>  1 file changed, 60 insertions(+), 47 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 3b5dc21b323c..46d2cfc30823 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -5526,6 +5526,29 @@ static ssize_t shmem_enabled_store(struct kobject *kobj,
>  struct kobj_attribute shmem_enabled_attr = __ATTR_RW(shmem_enabled);
>  static DEFINE_SPINLOCK(huge_shmem_orders_lock);
>
> +enum huge_shmem_enabled_mode {
> +	HUGE_SHMEM_ENABLED_ALWAYS = 0,
> +	HUGE_SHMEM_ENABLED_INHERIT,
> +	HUGE_SHMEM_ENABLED_WITHIN_SIZE,
> +	HUGE_SHMEM_ENABLED_ADVISE,
> +	HUGE_SHMEM_ENABLED_NEVER,
> +};
> +
> +static const char * const huge_shmem_enabled_mode_strings[] = {
> +	[HUGE_SHMEM_ENABLED_ALWAYS]      = "always",
> +	[HUGE_SHMEM_ENABLED_INHERIT]     = "inherit",
> +	[HUGE_SHMEM_ENABLED_WITHIN_SIZE] = "within_size",
> +	[HUGE_SHMEM_ENABLED_ADVISE]      = "advise",
> +	[HUGE_SHMEM_ENABLED_NEVER]       = "never",
> +};
> +
> +static unsigned long * const huge_shmem_orders_by_mode[] = {
> +	[HUGE_SHMEM_ENABLED_ALWAYS]      = &huge_shmem_orders_always,
> +	[HUGE_SHMEM_ENABLED_INHERIT]     = &huge_shmem_orders_inherit,
> +	[HUGE_SHMEM_ENABLED_WITHIN_SIZE] = &huge_shmem_orders_within_size,
> +	[HUGE_SHMEM_ENABLED_ADVISE]      = &huge_shmem_orders_madvise,
> +};

As Baolin suggested, we can probably rename these for bervity.

We know it's shmem, as it's in shmem.c :) so drop that.

huge_mode, huge_mode_strings, huge_mode_orders seems good to me?

> +
>  static ssize_t thpsize_shmem_enabled_show(struct kobject *kobj,
>  					  struct kobj_attribute *attr, char *buf)
>  {
> @@ -5546,63 +5569,53 @@ static ssize_t thpsize_shmem_enabled_show(struct kobject *kobj,
>  	return sysfs_emit(buf, "%s\n", output);
>  }
>
> +static bool set_shmem_enabled_mode(int order, enum huge_shmem_enabled_mode mode)
> +{
> +	bool changed = false;
> +	enum huge_shmem_enabled_mode idx;
> +
> +	spin_lock(&huge_shmem_orders_lock);
> +	for (idx = 0; idx < ARRAY_SIZE(huge_shmem_orders_by_mode); idx++) {
> +		if (idx == mode)
> +			changed |= !__test_and_set_bit(order, huge_shmem_orders_by_mode[idx]);
> +		else
> +			changed |= __test_and_clear_bit(order, huge_shmem_orders_by_mode[idx]);
> +	}
> +	spin_unlock(&huge_shmem_orders_lock);
> +
> +	return changed;
> +}
> +

Thanks for separating this out! :)

>  static ssize_t thpsize_shmem_enabled_store(struct kobject *kobj,
>  					   struct kobj_attribute *attr,
>  					   const char *buf, size_t count)
>  {
>  	int order = to_thpsize(kobj)->order;
> -	ssize_t ret = count;
> -
> -	if (sysfs_streq(buf, "always")) {
> -		spin_lock(&huge_shmem_orders_lock);
> -		clear_bit(order, &huge_shmem_orders_inherit);
> -		clear_bit(order, &huge_shmem_orders_madvise);
> -		clear_bit(order, &huge_shmem_orders_within_size);
> -		set_bit(order, &huge_shmem_orders_always);
> -		spin_unlock(&huge_shmem_orders_lock);
> -	} else if (sysfs_streq(buf, "inherit")) {
> -		/* Do not override huge allocation policy with non-PMD sized mTHP */
> -		if (shmem_huge == SHMEM_HUGE_FORCE && !is_pmd_order(order))
> -			return -EINVAL;
> +	int mode;
>
> -		spin_lock(&huge_shmem_orders_lock);
> -		clear_bit(order, &huge_shmem_orders_always);
> -		clear_bit(order, &huge_shmem_orders_madvise);
> -		clear_bit(order, &huge_shmem_orders_within_size);
> -		set_bit(order, &huge_shmem_orders_inherit);
> -		spin_unlock(&huge_shmem_orders_lock);
> -	} else if (sysfs_streq(buf, "within_size")) {
> -		spin_lock(&huge_shmem_orders_lock);
> -		clear_bit(order, &huge_shmem_orders_always);
> -		clear_bit(order, &huge_shmem_orders_inherit);
> -		clear_bit(order, &huge_shmem_orders_madvise);
> -		set_bit(order, &huge_shmem_orders_within_size);
> -		spin_unlock(&huge_shmem_orders_lock);
> -	} else if (sysfs_streq(buf, "advise")) {
> -		spin_lock(&huge_shmem_orders_lock);
> -		clear_bit(order, &huge_shmem_orders_always);
> -		clear_bit(order, &huge_shmem_orders_inherit);
> -		clear_bit(order, &huge_shmem_orders_within_size);
> -		set_bit(order, &huge_shmem_orders_madvise);
> -		spin_unlock(&huge_shmem_orders_lock);
> -	} else if (sysfs_streq(buf, "never")) {
> -		spin_lock(&huge_shmem_orders_lock);
> -		clear_bit(order, &huge_shmem_orders_always);
> -		clear_bit(order, &huge_shmem_orders_inherit);
> -		clear_bit(order, &huge_shmem_orders_within_size);
> -		clear_bit(order, &huge_shmem_orders_madvise);
> -		spin_unlock(&huge_shmem_orders_lock);
> -	} else {
> -		ret = -EINVAL;
> -	}
> +	mode = sysfs_match_string(huge_shmem_enabled_mode_strings, buf);
> +	if (mode < 0)
> +		return mode;
>
> -	if (ret > 0) {
> -		int err = start_stop_khugepaged();
> +	/* Do not override huge allocation policy with non-PMD sized mTHP */
> +	if (mode == HUGE_SHMEM_ENABLED_INHERIT &&
> +	    shmem_huge == SHMEM_HUGE_FORCE && !is_pmd_order(order))
> +		return -EINVAL;
>
> +	if (set_shmem_enabled_mode(order, mode)) {
> +		int err = start_stop_khugepaged();
>  		if (err)
> -			ret = err;
> +			return err;
> +	} else {
> +		/*
> +		 * Recalculate watermarks even when the mode hasn't changed
> +		 * to preserve the legacy behavior, as this is always called
> +		 * inside start_stop_khugepaged().
> +		 */
> +		set_recommended_min_free_kbytes();
>  	}
> -	return ret;
> +
> +	return count;
>  }
>
>  struct kobj_attribute thpsize_shmem_enabled_attr =
> --
> 2.25.1
>
>