[Patch v3 0/2] mm/huge_memory: cleanup for pmd folio installation

[Patch v3 0/2] mm/huge_memory: cleanup for pmd folio installation

[Wei Yang]

This is mostly a resend of previous two separate patches [1][2].

Since they both modify the same file, there would be some conflict if just
apply one of it. To make reviewing smoothly, they are resend together as
suggested by Zi Yan.

Patch [1] add pmd folio to ds_queue during do_huge_zero_wp_pmd() which is missed
Patch [2] unify pmd folio installation in collapse_huge_page() like other places

No code change after previous version, so I preserve the RB and Acked-by.

They are rebased on current akpm/mm-new branch with base commit:

    1de81dd7733c 2025-10-07 mm/page_alloc: batch page freeing in free_frozen_page_commit

[1]: https://lkml.kernel.org/r/20251002013825.20448-1-richard.weiyang@gmail.com
[2]: https://lkml.kernel.org/r/20251007005022.24413-1-richard.weiyang@gmail.com

Wei Yang (2):
  mm/huge_memory: add pmd folio to ds_queue in do_huge_zero_wp_pmd()
  mm/khugepaged: unify pmd folio installation with map_anon_folio_pmd()

 include/linux/huge_mm.h |  7 +++++++
 mm/huge_memory.c        | 14 ++++++++++----
 mm/khugepaged.c         |  9 +--------
 3 files changed, 18 insertions(+), 12 deletions(-)

-- 
2.34.1

[Patch v3 1/2] mm/huge_memory: add pmd folio to ds_queue in do_huge_zero_wp_pmd()

[Wei Yang]

We add pmd folio into ds_queue on the first page fault in
__do_huge_pmd_anonymous_page(), so that we can split it in case of
memory pressure. This should be the same for a pmd folio during wp
page fault.

Commit 1ced09e0331f ("mm: allocate THP on hugezeropage wp-fault") miss
to add it to ds_queue, which means system may not reclaim enough memory
in case of memory pressure even the pmd folio is under used.

Move deferred_split_folio() into map_anon_folio_pmd() to make the pmd
folio installation consistent.

Fixes: 1ced09e0331f ("mm: allocate THP on hugezeropage wp-fault")
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Acked-by: Usama Arif <usamaarif642@gmail.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>

---
v3:
  * rebase on latest mm-new
  * gather rb and acked-by
v2:
  * add fix, cc stable and put description about the flow of current
    code
  * move deferred_split_folio() into map_anon_folio_pmd()
---
 mm/huge_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 002922bb6e42..e86699306c5e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1317,6 +1317,7 @@ static void map_anon_folio_pmd(struct folio *folio, pmd_t *pmd,
 	count_vm_event(THP_FAULT_ALLOC);
 	count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_ALLOC);
 	count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC);
+	deferred_split_folio(folio, false);
 }
 
 static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf)
@@ -1357,7 +1358,6 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf)
 		pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
 		map_anon_folio_pmd(folio, vmf->pmd, vma, haddr);
 		mm_inc_nr_ptes(vma->vm_mm);
-		deferred_split_folio(folio, false);
 		spin_unlock(vmf->ptl);
 	}
 
-- 
2.34.1

[Patch v3 2/2] mm/khugepaged: unify pmd folio installation with map_anon_folio_pmd()

[Wei Yang]

Currently we install pmd folio with map_anon_folio_pmd() in
__do_huge_pmd_anonymous_page() and do_huge_zero_wp_pmd(). While in
collapse_huge_page(), it is done with identical code except statistics
adjustment.

Unify the process with map_anon_folio_pmd() to install pmd folio. Split
it to map_anon_folio_pmd_pf() and map_anon_folio_pmd_nopf() to be used
in page fault or not respectively.

No functional change is intended.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: Lance Yang <lance.yang@linux.dev>

---
v3:
  * add static inline and put bracket into separate lines
  * rebase on latest mm-new
v2:
  * split map_anon_folio_pmd_[no]pf() suggested by Matthew
---
 include/linux/huge_mm.h |  7 +++++++
 mm/huge_memory.c        | 14 ++++++++++----
 mm/khugepaged.c         |  9 +--------
 3 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index bb48cb50c0ec..588e3522a1d0 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -542,6 +542,8 @@ void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address,
 			   pmd_t *pmd, bool freeze);
 bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr,
 			   pmd_t *pmdp, struct folio *folio);
+void map_anon_folio_pmd_nopf(struct folio *folio, pmd_t *pmd,
+		struct vm_area_struct *vma, unsigned long haddr);
 
 #else /* CONFIG_TRANSPARENT_HUGEPAGE */
 
@@ -633,6 +635,11 @@ static inline bool unmap_huge_pmd_locked(struct vm_area_struct *vma,
 	return false;
 }
 
+static inline void map_anon_folio_pmd_nopf(struct folio *folio, pmd_t *pmd,
+		struct vm_area_struct *vma, unsigned long haddr)
+{
+}
+
 #define split_huge_pud(__vma, __pmd, __address)	\
 	do { } while (0)
 
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e86699306c5e..09198906667b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1302,7 +1302,7 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
 	return folio;
 }
 
-static void map_anon_folio_pmd(struct folio *folio, pmd_t *pmd,
+void map_anon_folio_pmd_nopf(struct folio *folio, pmd_t *pmd,
 		struct vm_area_struct *vma, unsigned long haddr)
 {
 	pmd_t entry;
@@ -1313,11 +1313,17 @@ static void map_anon_folio_pmd(struct folio *folio, pmd_t *pmd,
 	folio_add_lru_vma(folio, vma);
 	set_pmd_at(vma->vm_mm, haddr, pmd, entry);
 	update_mmu_cache_pmd(vma, haddr, pmd);
+	deferred_split_folio(folio, false);
+}
+
+static void map_anon_folio_pmd_pf(struct folio *folio, pmd_t *pmd,
+		struct vm_area_struct *vma, unsigned long haddr)
+{
+	map_anon_folio_pmd_nopf(folio, pmd, vma, haddr);
 	add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
 	count_vm_event(THP_FAULT_ALLOC);
 	count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_ALLOC);
 	count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC);
-	deferred_split_folio(folio, false);
 }
 
 static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf)
@@ -1356,7 +1362,7 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf)
 			return ret;
 		}
 		pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
-		map_anon_folio_pmd(folio, vmf->pmd, vma, haddr);
+		map_anon_folio_pmd_pf(folio, vmf->pmd, vma, haddr);
 		mm_inc_nr_ptes(vma->vm_mm);
 		spin_unlock(vmf->ptl);
 	}
@@ -1962,7 +1968,7 @@ static vm_fault_t do_huge_zero_wp_pmd(struct vm_fault *vmf)
 	if (ret)
 		goto release;
 	(void)pmdp_huge_clear_flush(vma, haddr, vmf->pmd);
-	map_anon_folio_pmd(folio, vmf->pmd, vma, haddr);
+	map_anon_folio_pmd_pf(folio, vmf->pmd, vma, haddr);
 	goto unlock;
 release:
 	folio_put(folio);
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index abe54f0043c7..e947b96e1443 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1224,17 +1224,10 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
 	__folio_mark_uptodate(folio);
 	pgtable = pmd_pgtable(_pmd);
 
-	_pmd = folio_mk_pmd(folio, vma->vm_page_prot);
-	_pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
-
 	spin_lock(pmd_ptl);
 	BUG_ON(!pmd_none(*pmd));
-	folio_add_new_anon_rmap(folio, vma, address, RMAP_EXCLUSIVE);
-	folio_add_lru_vma(folio, vma);
 	pgtable_trans_huge_deposit(mm, pmd, pgtable);
-	set_pmd_at(mm, address, pmd, _pmd);
-	update_mmu_cache_pmd(vma, address, pmd);
-	deferred_split_folio(folio, false);
+	map_anon_folio_pmd_nopf(folio, pmd, vma, address);
 	spin_unlock(pmd_ptl);
 
 	folio = NULL;
-- 
2.34.1

Re: [Patch v3 2/2] mm/khugepaged: unify pmd folio installation with map_anon_folio_pmd()

[Dev Jain]

On 08/10/25 3:24 pm, Wei Yang wrote:
> Currently we install pmd folio with map_anon_folio_pmd() in
> __do_huge_pmd_anonymous_page() and do_huge_zero_wp_pmd(). While in
> collapse_huge_page(), it is done with identical code except statistics
> adjustment.
>
> Unify the process with map_anon_folio_pmd() to install pmd folio. Split
> it to map_anon_folio_pmd_pf() and map_anon_folio_pmd_nopf() to be used
> in page fault or not respectively.
>
> No functional change is intended.
>
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Lance Yang <lance.yang@linux.dev>
> Cc: Dev Jain <dev.jain@arm.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Usama Arif <usamaarif642@gmail.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Acked-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Acked-by: Lance Yang <lance.yang@linux.dev>
>
> ---

LGTM

Reviewed-by: Dev Jain <dev.jain@arm.com>

Re: [Patch v3 2/2] mm/khugepaged: unify pmd folio installation with map_anon_folio_pmd()

[David Hildenbrand]

On 08.10.25 11:54, Wei Yang wrote:
> Currently we install pmd folio with map_anon_folio_pmd() in
> __do_huge_pmd_anonymous_page() and do_huge_zero_wp_pmd(). While in
> collapse_huge_page(), it is done with identical code except statistics
> adjustment.
> 
> Unify the process with map_anon_folio_pmd() to install pmd folio. Split
> it to map_anon_folio_pmd_pf() and map_anon_folio_pmd_nopf() to be used
> in page fault or not respectively.
> 
> No functional change is intended.
> 
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Lance Yang <lance.yang@linux.dev>
> Cc: Dev Jain <dev.jain@arm.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Usama Arif <usamaarif642@gmail.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Acked-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Acked-by: Lance Yang <lance.yang@linux.dev>
> 
> ---
> v3:
>    * add static inline and put bracket into separate lines
>    * rebase on latest mm-new
> v2:
>    * split map_anon_folio_pmd_[no]pf() suggested by Matthew
> ---
>   include/linux/huge_mm.h |  7 +++++++
>   mm/huge_memory.c        | 14 ++++++++++----
>   mm/khugepaged.c         |  9 +--------
>   3 files changed, 18 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index bb48cb50c0ec..588e3522a1d0 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -542,6 +542,8 @@ void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address,
>   			   pmd_t *pmd, bool freeze);
>   bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr,
>   			   pmd_t *pmdp, struct folio *folio);
> +void map_anon_folio_pmd_nopf(struct folio *folio, pmd_t *pmd,
> +		struct vm_area_struct *vma, unsigned long haddr);
>   
>   #else /* CONFIG_TRANSPARENT_HUGEPAGE */
>   
> @@ -633,6 +635,11 @@ static inline bool unmap_huge_pmd_locked(struct vm_area_struct *vma,
>   	return false;
>   }
>   
> +static inline void map_anon_folio_pmd_nopf(struct folio *folio, pmd_t *pmd,
> +		struct vm_area_struct *vma, unsigned long haddr)
> +{
> +}
> +

Thinking again, maybe you don't even need this stub? Any calling code 
should be guarded by CONFIG_TRANSPARENT_HUGEPAGE.

-- 
Cheers

David / dhildenb

Re: [Patch v3 2/2] mm/khugepaged: unify pmd folio installation with map_anon_folio_pmd()

[Wei Yang]

On Wed, Oct 08, 2025 at 04:45:52PM +0200, David Hildenbrand wrote:
>On 08.10.25 11:54, Wei Yang wrote:
>> Currently we install pmd folio with map_anon_folio_pmd() in
>> __do_huge_pmd_anonymous_page() and do_huge_zero_wp_pmd(). While in
>> collapse_huge_page(), it is done with identical code except statistics
>> adjustment.
>> 
>> Unify the process with map_anon_folio_pmd() to install pmd folio. Split
>> it to map_anon_folio_pmd_pf() and map_anon_folio_pmd_nopf() to be used
>> in page fault or not respectively.
>> 
>> No functional change is intended.
>> 
>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Lance Yang <lance.yang@linux.dev>
>> Cc: Dev Jain <dev.jain@arm.com>
>> Cc: Zi Yan <ziy@nvidia.com>
>> Cc: Usama Arif <usamaarif642@gmail.com>
>> Cc: Matthew Wilcox <willy@infradead.org>
>> Acked-by: David Hildenbrand <david@redhat.com>
>> Reviewed-by: Zi Yan <ziy@nvidia.com>
>> Acked-by: Lance Yang <lance.yang@linux.dev>
>> 
>> ---
>> v3:
>>    * add static inline and put bracket into separate lines
>>    * rebase on latest mm-new
>> v2:
>>    * split map_anon_folio_pmd_[no]pf() suggested by Matthew
>> ---
>>   include/linux/huge_mm.h |  7 +++++++
>>   mm/huge_memory.c        | 14 ++++++++++----
>>   mm/khugepaged.c         |  9 +--------
>>   3 files changed, 18 insertions(+), 12 deletions(-)
>> 
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index bb48cb50c0ec..588e3522a1d0 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -542,6 +542,8 @@ void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address,
>>   			   pmd_t *pmd, bool freeze);
>>   bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr,
>>   			   pmd_t *pmdp, struct folio *folio);
>> +void map_anon_folio_pmd_nopf(struct folio *folio, pmd_t *pmd,
>> +		struct vm_area_struct *vma, unsigned long haddr);
>>   #else /* CONFIG_TRANSPARENT_HUGEPAGE */
>> @@ -633,6 +635,11 @@ static inline bool unmap_huge_pmd_locked(struct vm_area_struct *vma,
>>   	return false;
>>   }
>> +static inline void map_anon_folio_pmd_nopf(struct folio *folio, pmd_t *pmd,
>> +		struct vm_area_struct *vma, unsigned long haddr)
>> +{
>> +}
>> +
>
>Thinking again, maybe you don't even need this stub? Any calling code should
>be guarded by CONFIG_TRANSPARENT_HUGEPAGE.
>

I think you are right.

I have removed the stub and build with/out CONFIG_TRANSPARENT_HUGEPAGE, both
are fine.

@Andrew, would you mind removing the above static inline stub? Thanks.

>-- 
>Cheers
>
>David / dhildenb

-- 
Wei Yang
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