Re: [PATCH v2 2/2] mm: huge_memory: refactor thpsize_shmem_enabled_show() with helper arrays

[Lorenzo Stoakes]

(As I said in the 1/2)

Please don't send 2/2 in response to 1/2, and use a cover letter if you send
more than 1 patch!

On Wed, May 13, 2026 at 09:45:08AM +0000, ranxiaokai627@xxxxxxx wrote:
> From: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
>
> Replace the hardcoded if/else chain of test_bit() calls and string
> literals in thpsize_shmem_enabled_show() with a loop over
> huge_shmem_orders_by_mode[] and huge_shmem_enabled_mode_strings[] arrays.
>
> This makes thpsize_shmem_enabled_show() consistent with
> thpsize_shmem_enabled_store() and eliminates duplicated mode name strings.
>
> Signed-off-by: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>

The logic looks good, I wish we could de-duplicate. But for now maybe better to
get this refactored first.

So:

Reviewed-by: Lorenzo Stoakes <ljs@xxxxxxxxxx>

> ---
>  mm/shmem.c | 36 +++++++++++++++++++++++-------------
>  1 file changed, 23 insertions(+), 13 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 60cb10854f11..086762e6de71 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -5553,20 +5553,30 @@ static ssize_t thpsize_shmem_enabled_show(struct kobject *kobj,
>  					  struct kobj_attribute *attr, char *buf)
>  {
>  	int order = to_thpsize(kobj)->order;
> -	const char *output;
> -
> -	if (test_bit(order, &huge_shmem_orders_always))
> -		output = "[always] inherit within_size advise never";
> -	else if (test_bit(order, &huge_shmem_orders_inherit))
> -		output = "always [inherit] within_size advise never";
> -	else if (test_bit(order, &huge_shmem_orders_within_size))
> -		output = "always inherit [within_size] advise never";
> -	else if (test_bit(order, &huge_shmem_orders_madvise))
> -		output = "always inherit within_size [advise] never";
> -	else
> -		output = "always inherit within_size advise [never]";
> +	int active = HUGE_SHMEM_ENABLED_NEVER;
> +	int len = 0;
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(huge_shmem_orders_by_mode); i++) {
> +		if (test_bit(order, huge_shmem_orders_by_mode[i])) {
> +			active = i;
> +			break;
> +		}
> +	}
> +
> +	for (i = 0; i < ARRAY_SIZE(huge_shmem_enabled_mode_strings); i++) {
> +		if (i == active)
> +			len += sysfs_emit_at(buf, len, "[%s] ",
> +						huge_shmem_enabled_mode_strings[i]);
> +		else
> +			len += sysfs_emit_at(buf, len, "%s ",
> +						huge_shmem_enabled_mode_strings[i]);
> +	}
> +
> +	/* Replace trailing space with newline */
> +	buf[len - 1] = '\n';
>
> -	return sysfs_emit(buf, "%s\n", output);
> +	return len;
>  }

This is pretty mcuh a one-for-one copy/pasta of defrag_show(), I don't love that
we have the exact same code duplicated across two files like that.

You could write something like:

static ssize_t thp_sysfs_enabled_show(struct kobject *kobj,
	       struct kobj_attribute *attr, char *buf,
	       const char *names, int names_len,
	       const char *orders_by_mode, int orders_by_mode_len,
	       int default_mode)
{
	...
}

To abstract it, but that's kind of a horrible signature isn't it? :)

Could use a helper struct, but that feels a bit overkill for this hmm...

Really I wonder if we shouldn't have this in huge_memory.c anyway, it's a bit of
a weird thing to put it in mm/shmem.c, it's more huge pages than shmem imo.

Anyway. The logic itself looks fine so LGTM!

>
>  static ssize_t thpsize_shmem_enabled_store(struct kobject *kobj,
> --
> 2.25.1
>
>

Cheers, Lorenzo