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

[Lorenzo Stoakes]

On Fri, May 15, 2026 at 06:04:41AM +0000, ranxiaokai627@xxxxxxx wrote:
> >(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.

Well it'd probably be overkill :)

For the time being, let's not do that, and just get this change in (with other
changes suggested applied of course), so send a respin without that please.


I think it's more important to address the hideous duplication we have _right
now_ rather than optimising deduplicating this code :) we can always do that
later.

Cheers, Lorenzo

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