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

[Zi Yan <ziy@nvidia.com>]

On 20 Apr 2026, at 2:55, Baolin Wang wrote:

> 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.

You are right.

I will revert back to the old comment without “when configured in” like below.

	/*
	 * We cover the anon, shmem and the file-backed case here; file-backed
	 * hugepages 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.
	 */

>
> The code changes LGTM.

Thanks.

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


Best Regards,
Yan, Zi