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

[Baolin Wang]

CC Breno and Lorenzo

On 5/12/26 8:05 PM, ranxiaokai627@xxxxxxx wrote:
> From: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
>
> 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.
>
> Tested with selftests ./run_kselftest.sh -t mm:ksft_thp.sh,
> all test cases passed.
>
> Signed-off-by: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
> ---

Thanks for doing this.

>   mm/shmem.c | 88 ++++++++++++++++++++++++++----------------------------
>   1 file changed, 43 insertions(+), 45 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 3b5dc21b323c..0cc7872cc576 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,
> +};
> +
>   static ssize_t thpsize_shmem_enabled_show(struct kobject *kobj,
>   					  struct kobj_attribute *attr, char *buf)
>   {
> @@ -5551,57 +5574,32 @@ static ssize_t thpsize_shmem_enabled_store(struct kobject *kobj,
>   					   const char *buf, size_t count)
>   {
>   	int order = to_thpsize(kobj)->order;
> +	int mode, m;
>   	ssize_t ret = count;
> +	int err;
>   
> -	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;
> +	mode = sysfs_match_string(huge_shmem_enabled_mode_strings, buf);
> +	if (mode < 0)
> +		return -EINVAL;
>   
> -		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;
> +	/* 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;
> +
> +	spin_lock(&huge_shmem_orders_lock);
> +	for (m = 0; m < ARRAY_SIZE(huge_shmem_orders_by_mode); m++) {
> +		if (m == mode)
> +			set_bit(order, huge_shmem_orders_by_mode[m]);
> +		else
> +			clear_bit(order, huge_shmem_orders_by_mode[m]);
>   	}

We are already under the lock, so you can use non-atomic functions like 
commit 82d9ff648c6c does: __test_and_set_bit/__test_and_clear_bit.

> +	spin_unlock(&huge_shmem_orders_lock);
>   
> -	if (ret > 0) {
> -		int err = start_stop_khugepaged();
> +	err = start_stop_khugepaged();
> +	if (err)

Moreover, I think we can follow commit 82d9ff648c6c's approach: if 
nothing changed, we don't need to call start_stop_khugepaged().