Re: [PATCH 7.2 v3 04/12] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check in hugepage_pmd_enabled()

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 4/18/26 10:44 AM, Zi Yan wrote:
> Remove READ_ONLY_THP_FOR_FS and khugepaged for file-backed pmd-sized
> hugepages are enabled by the global transparent hugepage control.
> khugepaged can still be enabled by per-size control for anon and shmem when
> the global control is off.
> 
> Add shmem_hpage_pmd_enabled() stub for !CONFIG_SHMEM to remove
> IS_ENABLED(SHMEM) in hugepage_pmd_enabled().
> 
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> ---
>   include/linux/shmem_fs.h |  2 +-
>   mm/khugepaged.c          | 28 ++++++++++++++++------------
>   2 files changed, 17 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> index 1a345142af7d..dff8fb6ddac0 100644
> --- a/include/linux/shmem_fs.h
> +++ b/include/linux/shmem_fs.h
> @@ -127,7 +127,7 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
>   void shmem_truncate_range(struct inode *inode, loff_t start, uoff_t end);
>   int shmem_unuse(unsigned int type);
>   
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && defined(CONFIG_SHMEM)
>   unsigned long shmem_allowable_huge_orders(struct inode *inode,
>   				struct vm_area_struct *vma, pgoff_t index,
>   				loff_t write_end, bool shmem_huge_force);
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 1c0fdc81d276..718a2d06d1e6 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -406,18 +406,8 @@ static inline int collapse_test_exit_or_disable(struct mm_struct *mm)
>   		mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm);
>   }
>   
> -static bool hugepage_pmd_enabled(void)
> +static inline bool anon_hpage_pmd_enabled(void)
>   {
> -	/*
> -	 * We cover the anon, shmem and the file-backed case here; file-backed
> -	 * hugepages, when configured in, are determined by the global control.
> -	 * Anon pmd-sized hugepages are determined by the pmd-size control.
> -	 * Shmem pmd-sized hugepages are also determined by its pmd-size control,
> -	 * except when the global shmem_huge is set to SHMEM_HUGE_DENY.
> -	 */
> -	if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
> -	    hugepage_global_enabled())
> -		return true;
>   	if (test_bit(PMD_ORDER, &huge_anon_orders_always))
>   		return true;
>   	if (test_bit(PMD_ORDER, &huge_anon_orders_madvise))
> @@ -425,7 +415,21 @@ static bool hugepage_pmd_enabled(void)
>   	if (test_bit(PMD_ORDER, &huge_anon_orders_inherit) &&
>   	    hugepage_global_enabled())
>   		return true;
> -	if (IS_ENABLED(CONFIG_SHMEM) && shmem_hpage_pmd_enabled())
> +	return false;
> +}
> +
> +static bool hugepage_pmd_enabled(void)
> +{
> +	/*
> +	 * Anon, shmem and file-backed pmd-size hugepages are all determined by
> +	 * the global control. If the global control is off, anon and shmem
> +	 * pmd-sized hugepages are also determined by its per-size control.
> +	 */

Personally, I found the previous comments clearer to me. The statement 
"Anon, shmem pmd-size hugepages are all determined by the global 
control" seems somewhat confusing. For example, if 
hugepage_global_enabled() returns true but the pmd-sized sub-control is 
set to 'never', that means anon pmd-size hugepages are not allowed.

The code changes LGTM.

> +	if (hugepage_global_enabled())
> +		return true;
> +	if (anon_hpage_pmd_enabled())
> +		return true;
> +	if (shmem_hpage_pmd_enabled())
>   		return true;
>   	return false;
>   }