Re: [PATCH v2 2/2] mm: huge_memory: refactor defrag_show() to use defrag_flags[]

[Lorenzo Stoakes <ljs@kernel.org>]

On Wed, Apr 08, 2026 at 08:47:01AM -0700, Breno Leitao wrote:
> Replace the hardcoded if/else chain of test_bit() calls and string
> literals in defrag_show() with a loop over defrag_flags[] and
> defrag_mode_strings[] arrays introduced in the previous commit.
>
> This makes defrag_show() consistent with defrag_store() and eliminates
> the duplicated mode name strings.
>
> Acked-by: David Hildenbrand (Arm) <david@kernel.org>
> Tested-by: Lance Yang <lance.yang@linux.dev>
> Reviewed-by: Lance Yang <lance.yang@linux.dev>
> Reviewed-by: Barry Song <baohua@kernel.org>
> Signed-off-by: Breno Leitao <leitao@debian.org>

I almost made a comment, but then realised it was fine :P so LGTM and:

Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>

> ---
>  mm/huge_memory.c | 38 ++++++++++++++++++++++----------------
>  1 file changed, 22 insertions(+), 16 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 76f2d32428c7f..6993c6d8709dc 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -455,24 +455,30 @@ static const enum transparent_hugepage_flag defrag_flags[] = {
>  static ssize_t defrag_show(struct kobject *kobj,
>  			   struct kobj_attribute *attr, char *buf)
>  {
> -	const char *output;
> +	int active = DEFRAG_NEVER;
> +	int len = 0;
> +	int i;
>
> -	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
> -		     &transparent_hugepage_flags))
> -		output = "[always] defer defer+madvise madvise never";
> -	else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
> -			  &transparent_hugepage_flags))
> -		output = "always [defer] defer+madvise madvise never";
> -	else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG,
> -			  &transparent_hugepage_flags))
> -		output = "always defer [defer+madvise] madvise never";
> -	else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG,
> -			  &transparent_hugepage_flags))
> -		output = "always defer defer+madvise [madvise] never";
> -	else
> -		output = "always defer defer+madvise madvise [never]";
> +	for (i = 0; i < ARRAY_SIZE(defrag_flags); i++) {
> +		if (test_bit(defrag_flags[i], &transparent_hugepage_flags)) {
> +			active = i;
> +			break;
> +		}
> +	}
>
> -	return sysfs_emit(buf, "%s\n", output);
> +	for (i = 0; i < ARRAY_SIZE(defrag_mode_strings); i++) {
> +		if (i == active)
> +			len += sysfs_emit_at(buf, len, "[%s] ",
> +					     defrag_mode_strings[i]);
> +		else
> +			len += sysfs_emit_at(buf, len, "%s ",

I mean, we'll end up with a single trailing space, but I think we can
probably... oh wait hang on...

> +					     defrag_mode_strings[i]);
> +	}
> +
> +	/* Replace trailing space with newline */
> +	buf[len - 1] = '\n';

...OK :)

> +
> +	return len;
>  }
>
>  static ssize_t defrag_store(struct kobject *kobj,
>
> --
> 2.52.0
>

Cheers, Lorenzo