Re: [PATCH mm-unstable v15 12/13] mm/khugepaged: run khugepaged for all orders

[Nico Pache <npache@redhat.com>]

On 3/17/26 4:58 AM, Lorenzo Stoakes (Oracle) wrote:
> On Wed, Feb 25, 2026 at 08:26:50PM -0700, Nico Pache wrote:
>> From: Baolin Wang <baolin.wang@linux.alibaba.com>
>>
>> If any order (m)THP is enabled we should allow running khugepaged to
>> attempt scanning and collapsing mTHPs. In order for khugepaged to operate
>> when only mTHP sizes are specified in sysfs, we must modify the predicate
>> function that determines whether it ought to run to do so.
>>
>> This function is currently called hugepage_pmd_enabled(), this patch
>> renames it to hugepage_enabled() and updates the logic to check to
>> determine whether any valid orders may exist which would justify
>> khugepaged running.
>>
>> We must also update collapse_allowable_orders() to check all orders if
>> the vma is anonymous and the collapse is khugepaged.
>>
>> After this patch khugepaged mTHP collapse is fully enabled.
>>
>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>> Signed-off-by: Nico Pache <npache@redhat.com>
> 
> This looks good to me, so:
> 
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

Thanks!

> 
>> ---
>>  mm/khugepaged.c | 30 ++++++++++++++++++------------
>>  1 file changed, 18 insertions(+), 12 deletions(-)
>>
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index 388d3f2537e2..e8bfcc1d0c9a 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -434,23 +434,23 @@ 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 bool hugepage_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.
>> +	 * Anon hugepages are determined by its per-size mTHP control.
> 
> Well also PMD right? I mean this terminology sucks because in a sense mTHP
> includes PMD... :)

yeah kinda hard with our verbiage being so broad and overlapping some times.

> 
>>  	 * 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))
>> +	if (READ_ONCE(huge_anon_orders_always))
>>  		return true;
>> -	if (test_bit(PMD_ORDER, &huge_anon_orders_madvise))
>> +	if (READ_ONCE(huge_anon_orders_madvise))
>>  		return true;
>> -	if (test_bit(PMD_ORDER, &huge_anon_orders_inherit) &&
>> +	if (READ_ONCE(huge_anon_orders_inherit) &&
>>  	    hugepage_global_enabled())
>>  		return true;
>>  	if (IS_ENABLED(CONFIG_SHMEM) && shmem_hpage_pmd_enabled())
>> @@ -521,8 +521,14 @@ static unsigned int collapse_max_ptes_none(unsigned int order)
>>  static unsigned long collapse_allowable_orders(struct vm_area_struct *vma,
>>  			vm_flags_t vm_flags, bool is_khugepaged)
>>  {
>> +	unsigned long orders;
>>  	enum tva_type tva_flags = is_khugepaged ? TVA_KHUGEPAGED : TVA_FORCED_COLLAPSE;
>> -	unsigned long orders = BIT(HPAGE_PMD_ORDER);
>> +
>> +	/* If khugepaged is scanning an anonymous vma, allow mTHP collapse */
>> +	if (is_khugepaged && vma_is_anonymous(vma))
>> +		orders = THP_ORDERS_ALL_ANON;
>> +	else
>> +		orders = BIT(HPAGE_PMD_ORDER);
>>
>>  	return thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
>>  }
>> @@ -531,7 +537,7 @@ void khugepaged_enter_vma(struct vm_area_struct *vma,
>>  			  vm_flags_t vm_flags)
>>  {
>>  	if (!mm_flags_test(MMF_VM_HUGEPAGE, vma->vm_mm) &&
>> -	    hugepage_pmd_enabled()) {
>> +	    hugepage_enabled()) {
>>  		if (collapse_allowable_orders(vma, vm_flags, /*is_khugepaged=*/true))
>>  			__khugepaged_enter(vma->vm_mm);
>>  	}
>> @@ -2929,7 +2935,7 @@ static unsigned int collapse_scan_mm_slot(unsigned int pages, enum scan_result *
>>
>>  static int khugepaged_has_work(void)
>>  {
>> -	return !list_empty(&khugepaged_scan.mm_head) && hugepage_pmd_enabled();
>> +	return !list_empty(&khugepaged_scan.mm_head) && hugepage_enabled();
>>  }
>>
>>  static int khugepaged_wait_event(void)
>> @@ -3002,7 +3008,7 @@ static void khugepaged_wait_work(void)
>>  		return;
>>  	}
>>
>> -	if (hugepage_pmd_enabled())
>> +	if (hugepage_enabled())
>>  		wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
>>  }
>>
>> @@ -3033,7 +3039,7 @@ static void set_recommended_min_free_kbytes(void)
>>  	int nr_zones = 0;
>>  	unsigned long recommended_min;
>>
>> -	if (!hugepage_pmd_enabled()) {
>> +	if (!hugepage_enabled()) {
>>  		calculate_min_free_kbytes();
>>  		goto update_wmarks;
>>  	}
>> @@ -3083,7 +3089,7 @@ int start_stop_khugepaged(void)
>>  	int err = 0;
>>
>>  	mutex_lock(&khugepaged_mutex);
>> -	if (hugepage_pmd_enabled()) {
>> +	if (hugepage_enabled()) {
>>  		if (!khugepaged_thread)
>>  			khugepaged_thread = kthread_run(khugepaged, NULL,
>>  							"khugepaged");
>> @@ -3109,7 +3115,7 @@ int start_stop_khugepaged(void)
>>  void khugepaged_min_free_kbytes_update(void)
>>  {
>>  	mutex_lock(&khugepaged_mutex);
>> -	if (hugepage_pmd_enabled() && khugepaged_thread)
>> +	if (hugepage_enabled() && khugepaged_thread)
>>  		set_recommended_min_free_kbytes();
>>  	mutex_unlock(&khugepaged_mutex);
>>  }
>> --
>> 2.53.0
>>
>