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

[ranxiaokai627]

>(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!

Thanks for the guidance.
I will do that in the next verison.

>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!

Yes, after this patch is applied, the read/write handlers for the
shmem_enabled and enabled interfaces will have a lot of duplicated code.
I will continue to investigate whether we can abstract a more generic
function to handle both interfaces.
Introducing a helper struct as a parameter is a good inspiration.

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