Re: [PATCH v8 07/14] mm: shmem: allow THP support determination at folio allocation time

[Zi Yan]

On Thu Sep 17, 2026 at 9:45 PM EDT, Luiz Capitulino wrote:
> In order to enable THP support in shmem today, besides the user
> configuration required, the CPU must support PMD-sized pages. This
> is the case because of the following has_transparent_hugepage()
> usage:
>
> - shmem_parse_one() and shmem_parse_huge(): Check if THP is built-in and
>   if the CPU supports PMD-sized pages
>
> - shmem_init(): Since the CONFIG_TRANSPARENT_HUGEPAGE guard is outside
>   the code block calling has_transparent_hugepage(), the
>   has_transparent_hugepage() call is exclusively checking if the CPU
>   supports PMD-sized pages
>
> While it's necessary to check if CONFIG_TRANSPARENT_HUGEPAGE is enabled
> in all cases, shmem can determine THP size support at folio allocation
> time. Therefore, drop the has_transparent_hugepage() usage listed above
> while keeping the CONFIG_TRANSPARENT_HUGEPAGE checks.
>
> Additionally, we need to check if PMD size order is supported in
> shmem_getattr(). Use pgtable_has_pmd_leaves() for that.
>
> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Luiz Capitulino <luizcap@xxxxxxxxxx>
> ---
>  mm/shmem.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 776dff8a848e..930657d05375 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -690,7 +690,7 @@ static int shmem_parse_huge(const char *str)
>  	else
>  		return -EINVAL;
>  
> -	if (!has_transparent_hugepage() &&
> +	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
>  	    huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY)
>  		return -EINVAL;

This can be deleted, since shmem_parse_huge() is guarded by
CONFIG_TRANSPARENT_HUGEPAGE and after the change the if is always false
under that guard.

Otherwise, LGTM. With the above code deleted, feel free to add

Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>



-- 
Best Regards,
Yan, Zi