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 4/20/26 10:57 PM, Zi Yan wrote:
> 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.
> 	 */

Thanks. With that, feel free to add:
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>