linux-kernel - Re: [PATCH 07/11] mm: shmem: use pgtable_has_pmd

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Message-ID: <e7514940-1330-4c4c-84f8-fb9d66fff80d@linux.alibaba.com>
Date: Tue, 16 Dec 2025 15:52:09 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Luiz Capitulino <luizcap@...hat.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, david@...nel.org
Cc: ryan.roberts@....com, akpm@...ux-foundation.org,
 lorenzo.stoakes@...cle.com
Subject: Re: [PATCH 07/11] mm: shmem: use pgtable_has_pmd_leaves()



On 2025/12/16 05:16, Luiz Capitulino wrote:
> Shmem uses has_transparent_hugepage() to check if PMD-sized pages are
> supported, use pgtable_has_pmd_leaves() instead.
> 
> Signed-off-by: Luiz Capitulino <luizcap@...hat.com>
> ---
>   mm/shmem.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index b329b5302c48..ad5825667b49 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -689,7 +689,8 @@ static int shmem_parse_huge(const char *str)
>   	else
>   		return -EINVAL;
>   
> -	if (!has_transparent_hugepage() &&
> +	if (!(IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
> +	      pgtable_has_pmd_leaves()) &&
>   	    huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY)
>   		return -EINVAL;
>   
> @@ -4655,7 +4656,7 @@ static int shmem_parse_one(struct fs_context *fc, struct fs_parameter *param)
>   		ctx->huge = result.uint_32;
>   		if (ctx->huge != SHMEM_HUGE_NEVER &&
>   		    !(IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
> -		      has_transparent_hugepage()))
> +		      pgtable_has_pmd_leaves()))
>   			goto unsupported_parameter;
>   		ctx->seen |= SHMEM_SEEN_HUGE;
>   		break;
> @@ -5439,7 +5440,7 @@ void __init shmem_init(void)
>   #endif
>   
>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -	if (has_transparent_hugepage() && shmem_huge > SHMEM_HUGE_DENY)
> +	if (pgtable_has_pmd_leaves() && shmem_huge > SHMEM_HUGE_DENY)

Using pgtable_has_pmd_leaves() here is a bit confusing because the 
definition of pgtable_has_pmd_leaves() is: it returns true if the CPU 
supports PMD-sized pages and false otherwise.

However, tmpfs and shmem already support other sizes of large folios, 
not just PMD-sized large folios.

So, for me, using has_transparent_hugepage() to check would be at least 
clearer (even though it doesn't change the functionality).