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

Zi Yan
2026-04-20T14:58:08Z

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