Add device-private THP support to reverse mapping infrastructure,
enabling proper handling during migration and walk operations.

The key changes are:
- add_migration_pmd()/remove_migration_pmd(): Handle device-private
  entries during folio migration and splitting
- page_vma_mapped_walk(): Recognize device-private THP entries during
  VMA traversal operations

This change supports folio splitting and migration operations on
device-private entries.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Mika Penttilä <mpenttil@redhat.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Francois Dugast <francois.dugast@intel.com>

Signed-off-by: Balbir Singh <balbirs@nvidia.com>
---
 mm/damon/ops-common.c | 20 +++++++++++++++++---
 mm/huge_memory.c      | 16 +++++++++++++++-
 mm/page_idle.c        |  5 +++--
 mm/page_vma_mapped.c  | 12 ++++++++++--
 mm/rmap.c             | 19 ++++++++++++++++---
 5 files changed, 61 insertions(+), 11 deletions(-)

diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
index 998c5180a603..eda4de553611 100644
--- a/mm/damon/ops-common.c
+++ b/mm/damon/ops-common.c
@@ -75,12 +75,24 @@ void damon_ptep_mkold(pte_t *pte, struct vm_area_struct *vma, unsigned long addr
 void damon_pmdp_mkold(pmd_t *pmd, struct vm_area_struct *vma, unsigned long addr)
 {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	struct folio *folio = damon_get_folio(pmd_pfn(pmdp_get(pmd)));
+	pmd_t pmdval = pmdp_get(pmd);
+	struct folio *folio;
+	bool young = false;
+	unsigned long pfn;
+
+	if (likely(pmd_present(pmdval)))
+		pfn = pmd_pfn(pmdval);
+	else
+		pfn = swp_offset_pfn(pmd_to_swp_entry(pmdval));
 
+	folio = damon_get_folio(pfn);
 	if (!folio)
 		return;
 
-	if (pmdp_clear_young_notify(vma, addr, pmd))
+	if (likely(pmd_present(pmdval)))
+		young |= pmdp_clear_young_notify(vma, addr, pmd);
+	young |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE);
+	if (young)
 		folio_set_young(folio);
 
 	folio_set_idle(folio);
@@ -203,7 +215,9 @@ static bool damon_folio_young_one(struct folio *folio,
 				mmu_notifier_test_young(vma->vm_mm, addr);
 		} else {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-			*accessed = pmd_young(pmdp_get(pvmw.pmd)) ||
+			pmd_t pmd = pmdp_get(pvmw.pmd);
+
+			*accessed = (pmd_present(pmd) && pmd_young(pmd)) ||
 				!folio_test_idle(folio) ||
 				mmu_notifier_test_young(vma->vm_mm, addr);
 #else
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 2af74e09b279..337d8e3dd837 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -4641,7 +4641,10 @@ int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
 		return 0;
 
 	flush_cache_range(vma, address, address + HPAGE_PMD_SIZE);
-	pmdval = pmdp_invalidate(vma, address, pvmw->pmd);
+	if (unlikely(!pmd_present(*pvmw->pmd)))
+		pmdval = pmdp_huge_get_and_clear(vma->vm_mm, address, pvmw->pmd);
+	else
+		pmdval = pmdp_invalidate(vma, address, pvmw->pmd);
 
 	/* See folio_try_share_anon_rmap_pmd(): invalidate PMD first. */
 	anon_exclusive = folio_test_anon(folio) && PageAnonExclusive(page);
@@ -4691,6 +4694,17 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
 	entry = pmd_to_swp_entry(*pvmw->pmd);
 	folio_get(folio);
 	pmde = folio_mk_pmd(folio, READ_ONCE(vma->vm_page_prot));
+
+	if (folio_is_device_private(folio)) {
+		if (pmd_write(pmde))
+			entry = make_writable_device_private_entry(
+							page_to_pfn(new));
+		else
+			entry = make_readable_device_private_entry(
+							page_to_pfn(new));
+		pmde = swp_entry_to_pmd(entry);
+	}
+
 	if (pmd_swp_soft_dirty(*pvmw->pmd))
 		pmde = pmd_mksoft_dirty(pmde);
 	if (is_writable_migration_entry(entry))
diff --git a/mm/page_idle.c b/mm/page_idle.c
index a82b340dc204..9030c31800ce 100644
--- a/mm/page_idle.c
+++ b/mm/page_idle.c
@@ -71,8 +71,9 @@ static bool page_idle_clear_pte_refs_one(struct folio *folio,
 				referenced |= ptep_test_and_clear_young(vma, addr, pvmw.pte);
 			referenced |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE);
 		} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
-			if (pmdp_clear_young_notify(vma, addr, pvmw.pmd))
-				referenced = true;
+			if (likely(pmd_present(pmdp_get(pvmw.pmd))))
+				referenced |= pmdp_clear_young_notify(vma, addr, pvmw.pmd);
+			referenced |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE);
 		} else {
 			/* unexpected pmd-mapped page? */
 			WARN_ON_ONCE(1);
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index e981a1a292d2..7ab46a2b4e15 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -250,12 +250,11 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 			pvmw->ptl = pmd_lock(mm, pvmw->pmd);
 			pmde = *pvmw->pmd;
 			if (!pmd_present(pmde)) {
-				swp_entry_t entry;
+				swp_entry_t entry = pmd_to_swp_entry(pmde);
 
 				if (!thp_migration_supported() ||
 				    !(pvmw->flags & PVMW_MIGRATION))
 					return not_found(pvmw);
-				entry = pmd_to_swp_entry(pmde);
 				if (!is_migration_entry(entry) ||
 				    !check_pmd(swp_offset_pfn(entry), pvmw))
 					return not_found(pvmw);
@@ -277,6 +276,15 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 			 * cannot return prematurely, while zap_huge_pmd() has
 			 * cleared *pmd but not decremented compound_mapcount().
 			 */
+			swp_entry_t entry;
+
+			entry = pmd_to_swp_entry(pmde);
+
+			if (is_device_private_entry(entry)) {
+				pvmw->ptl = pmd_lock(mm, pvmw->pmd);
+				return true;
+			}
+
 			if ((pvmw->flags & PVMW_SYNC) &&
 			    thp_vma_suitable_order(vma, pvmw->address,
 						   PMD_ORDER) &&
diff --git a/mm/rmap.c b/mm/rmap.c
index 236ceff5b276..6de1baf7a4f1 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1063,8 +1063,10 @@ static int page_vma_mkclean_one(struct page_vma_mapped_walk *pvmw)
 		} else {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 			pmd_t *pmd = pvmw->pmd;
-			pmd_t entry;
+			pmd_t entry = pmdp_get(pmd);
 
+			if (!pmd_present(entry))
+				continue;
 			if (!pmd_dirty(*pmd) && !pmd_write(*pmd))
 				continue;
 
@@ -2330,6 +2332,11 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 	while (page_vma_mapped_walk(&pvmw)) {
 		/* PMD-mapped THP migration entry */
 		if (!pvmw.pte) {
+#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
+			unsigned long pfn;
+			pmd_t pmdval;
+#endif
+
 			if (flags & TTU_SPLIT_HUGE_PMD) {
 				split_huge_pmd_locked(vma, pvmw.address,
 						      pvmw.pmd, true);
@@ -2338,8 +2345,14 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 				break;
 			}
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
-			subpage = folio_page(folio,
-				pmd_pfn(*pvmw.pmd) - folio_pfn(folio));
+			pmdval = pmdp_get(pvmw.pmd);
+			if (likely(pmd_present(pmdval)))
+				pfn = pmd_pfn(pmdval);
+			else
+				pfn = swp_offset_pfn(pmd_to_swp_entry(pmdval));
+
+			subpage = folio_page(folio, pfn - folio_pfn(folio));
+
 			VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) ||
 					!folio_test_pmd_mappable(folio), folio);
 
-- 
2.50.1

On Mon,  8 Sep 2025 10:04:36 +1000 Balbir Singh <balbirs@nvidia.com> wrote:

> Add device-private THP support to reverse mapping infrastructure,
> enabling proper handling during migration and walk operations.
> 
> The key changes are:
> - add_migration_pmd()/remove_migration_pmd(): Handle device-private
>   entries during folio migration and splitting
> - page_vma_mapped_walk(): Recognize device-private THP entries during
>   VMA traversal operations
> 
> This change supports folio splitting and migration operations on
> device-private entries.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
> Cc: Rakie Kim <rakie.kim@sk.com>
> Cc: Byungchul Park <byungchul@sk.com>
> Cc: Gregory Price <gourry@gourry.net>
> Cc: Ying Huang <ying.huang@linux.alibaba.com>
> Cc: Alistair Popple <apopple@nvidia.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
> Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
> Cc: Nico Pache <npache@redhat.com>
> Cc: Ryan Roberts <ryan.roberts@arm.com>
> Cc: Dev Jain <dev.jain@arm.com>
> Cc: Barry Song <baohua@kernel.org>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: Danilo Krummrich <dakr@kernel.org>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Simona Vetter <simona@ffwll.ch>
> Cc: Ralph Campbell <rcampbell@nvidia.com>
> Cc: Mika Penttilä <mpenttil@redhat.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: Francois Dugast <francois.dugast@intel.com>
> 
> Signed-off-by: Balbir Singh <balbirs@nvidia.com>
> ---
>  mm/damon/ops-common.c | 20 +++++++++++++++++---
>  mm/huge_memory.c      | 16 +++++++++++++++-
>  mm/page_idle.c        |  5 +++--
>  mm/page_vma_mapped.c  | 12 ++++++++++--
>  mm/rmap.c             | 19 ++++++++++++++++---
>  5 files changed, 61 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
> index 998c5180a603..eda4de553611 100644
> --- a/mm/damon/ops-common.c
> +++ b/mm/damon/ops-common.c
> @@ -75,12 +75,24 @@ void damon_ptep_mkold(pte_t *pte, struct vm_area_struct *vma, unsigned long addr
>  void damon_pmdp_mkold(pmd_t *pmd, struct vm_area_struct *vma, unsigned long addr)
>  {
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -	struct folio *folio = damon_get_folio(pmd_pfn(pmdp_get(pmd)));
> +	pmd_t pmdval = pmdp_get(pmd);
> +	struct folio *folio;
> +	bool young = false;
> +	unsigned long pfn;
> +
> +	if (likely(pmd_present(pmdval)))
> +		pfn = pmd_pfn(pmdval);
> +	else
> +		pfn = swp_offset_pfn(pmd_to_swp_entry(pmdval));
>  
> +	folio = damon_get_folio(pfn);
>  	if (!folio)
>  		return;
>  
> -	if (pmdp_clear_young_notify(vma, addr, pmd))
> +	if (likely(pmd_present(pmdval)))
> +		young |= pmdp_clear_young_notify(vma, addr, pmd);
> +	young |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE);
> +	if (young)
>  		folio_set_young(folio);
>  
>  	folio_set_idle(folio);
> @@ -203,7 +215,9 @@ static bool damon_folio_young_one(struct folio *folio,
>  				mmu_notifier_test_young(vma->vm_mm, addr);
>  		} else {
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -			*accessed = pmd_young(pmdp_get(pvmw.pmd)) ||
> +			pmd_t pmd = pmdp_get(pvmw.pmd);
> +
> +			*accessed = (pmd_present(pmd) && pmd_young(pmd)) ||
>  				!folio_test_idle(folio) ||
>  				mmu_notifier_test_young(vma->vm_mm, addr);

Could you please elaborate more about why the above change is needed on the
commit message?

For example, I found below from v3 of this patch series:

    pmd_pfn() does not work well with zone device entries, use
    pfn_pmd_entry_to_swap() for checking and comparison as for zone device
    entries.

Adding that kind of elaboration on the commit message would be helpful.

Also, seems the DAMON part change is not really required to be made together
with other changes.  If I'm not wrong, could you make DAMON part change as a
separate commit?

The code looks good to me.

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

[...]

On 9/12/25 11:59, SeongJae Park wrote:
> On Mon,  8 Sep 2025 10:04:36 +1000 Balbir Singh <balbirs@nvidia.com> wrote:
> 
>> Add device-private THP support to reverse mapping infrastructure,
>> enabling proper handling during migration and walk operations.
>>
>> The key changes are:
>> - add_migration_pmd()/remove_migration_pmd(): Handle device-private
>>   entries during folio migration and splitting
>> - page_vma_mapped_walk(): Recognize device-private THP entries during
>>   VMA traversal operations
>>
>> This change supports folio splitting and migration operations on
>> device-private entries.
>>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Zi Yan <ziy@nvidia.com>
>> Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
>> Cc: Rakie Kim <rakie.kim@sk.com>
>> Cc: Byungchul Park <byungchul@sk.com>
>> Cc: Gregory Price <gourry@gourry.net>
>> Cc: Ying Huang <ying.huang@linux.alibaba.com>
>> Cc: Alistair Popple <apopple@nvidia.com>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
>> Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
>> Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
>> Cc: Nico Pache <npache@redhat.com>
>> Cc: Ryan Roberts <ryan.roberts@arm.com>
>> Cc: Dev Jain <dev.jain@arm.com>
>> Cc: Barry Song <baohua@kernel.org>
>> Cc: Lyude Paul <lyude@redhat.com>
>> Cc: Danilo Krummrich <dakr@kernel.org>
>> Cc: David Airlie <airlied@gmail.com>
>> Cc: Simona Vetter <simona@ffwll.ch>
>> Cc: Ralph Campbell <rcampbell@nvidia.com>
>> Cc: Mika Penttilä <mpenttil@redhat.com>
>> Cc: Matthew Brost <matthew.brost@intel.com>
>> Cc: Francois Dugast <francois.dugast@intel.com>
>>
>> Signed-off-by: Balbir Singh <balbirs@nvidia.com>
>> ---
>>  mm/damon/ops-common.c | 20 +++++++++++++++++---
>>  mm/huge_memory.c      | 16 +++++++++++++++-
>>  mm/page_idle.c        |  5 +++--
>>  mm/page_vma_mapped.c  | 12 ++++++++++--
>>  mm/rmap.c             | 19 ++++++++++++++++---
>>  5 files changed, 61 insertions(+), 11 deletions(-)
>>
>> diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
>> index 998c5180a603..eda4de553611 100644
>> --- a/mm/damon/ops-common.c
>> +++ b/mm/damon/ops-common.c
>> @@ -75,12 +75,24 @@ void damon_ptep_mkold(pte_t *pte, struct vm_area_struct *vma, unsigned long addr
>>  void damon_pmdp_mkold(pmd_t *pmd, struct vm_area_struct *vma, unsigned long addr)
>>  {
>>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> -	struct folio *folio = damon_get_folio(pmd_pfn(pmdp_get(pmd)));
>> +	pmd_t pmdval = pmdp_get(pmd);
>> +	struct folio *folio;
>> +	bool young = false;
>> +	unsigned long pfn;
>> +
>> +	if (likely(pmd_present(pmdval)))
>> +		pfn = pmd_pfn(pmdval);
>> +	else
>> +		pfn = swp_offset_pfn(pmd_to_swp_entry(pmdval));
>>  
>> +	folio = damon_get_folio(pfn);
>>  	if (!folio)
>>  		return;
>>  
>> -	if (pmdp_clear_young_notify(vma, addr, pmd))
>> +	if (likely(pmd_present(pmdval)))
>> +		young |= pmdp_clear_young_notify(vma, addr, pmd);
>> +	young |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE);
>> +	if (young)
>>  		folio_set_young(folio);
>>  
>>  	folio_set_idle(folio);
>> @@ -203,7 +215,9 @@ static bool damon_folio_young_one(struct folio *folio,
>>  				mmu_notifier_test_young(vma->vm_mm, addr);
>>  		} else {
>>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> -			*accessed = pmd_young(pmdp_get(pvmw.pmd)) ||
>> +			pmd_t pmd = pmdp_get(pvmw.pmd);
>> +
>> +			*accessed = (pmd_present(pmd) && pmd_young(pmd)) ||
>>  				!folio_test_idle(folio) ||
>>  				mmu_notifier_test_young(vma->vm_mm, addr);
> 
> Could you please elaborate more about why the above change is needed on the
> commit message?
> 
> For example, I found below from v3 of this patch series:
> 
>     pmd_pfn() does not work well with zone device entries, use
>     pfn_pmd_entry_to_swap() for checking and comparison as for zone device
>     entries.
> 
> Adding that kind of elaboration on the commit message would be helpful.
> 
> Also, seems the DAMON part change is not really required to be made together
> with other changes.  If I'm not wrong, could you make DAMON part change as a
> separate commit?
> 
> The code looks good to me.
> 
> Reviewed-by: SeongJae Park <sj@kernel.org>
> 
> 

Thanks SJ!

v3 had a separate flag during page vma mapped walk, so the walkers had to opt-in
with a flag, I removed that after David's review feedback

This change is required because we now support large folios in device private
and hence the DAMON changes are included in this patch

Balbir

On 08.09.25 02:04, Balbir Singh wrote:

subject:

"mm/rmap: rmap and migration support for device-private PMD entries"


> Add device-private THP support to reverse mapping infrastructure,
> enabling proper handling during migration and walk operations.
> 
> The key changes are:
> - add_migration_pmd()/remove_migration_pmd(): Handle device-private
>    entries during folio migration and splitting
> - page_vma_mapped_walk(): Recognize device-private THP entries during
>    VMA traversal operations
> 
> This change supports folio splitting and migration operations on
> device-private entries.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
> Cc: Rakie Kim <rakie.kim@sk.com>
> Cc: Byungchul Park <byungchul@sk.com>
> Cc: Gregory Price <gourry@gourry.net>
> Cc: Ying Huang <ying.huang@linux.alibaba.com>
> Cc: Alistair Popple <apopple@nvidia.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
> Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
> Cc: Nico Pache <npache@redhat.com>
> Cc: Ryan Roberts <ryan.roberts@arm.com>
> Cc: Dev Jain <dev.jain@arm.com>
> Cc: Barry Song <baohua@kernel.org>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: Danilo Krummrich <dakr@kernel.org>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Simona Vetter <simona@ffwll.ch>
> Cc: Ralph Campbell <rcampbell@nvidia.com>
> Cc: Mika Penttilä <mpenttil@redhat.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: Francois Dugast <francois.dugast@intel.com>
> 
> Signed-off-by: Balbir Singh <balbirs@nvidia.com>
> ---

[...]


> +++ b/mm/page_vma_mapped.c
> @@ -250,12 +250,11 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>   			pvmw->ptl = pmd_lock(mm, pvmw->pmd);
>   			pmde = *pvmw->pmd;
>   			if (!pmd_present(pmde)) {
> -				swp_entry_t entry;
> +				swp_entry_t entry = pmd_to_swp_entry(pmde);
>   
>   				if (!thp_migration_supported() ||
>   				    !(pvmw->flags & PVMW_MIGRATION))
>   					return not_found(pvmw);
> -				entry = pmd_to_swp_entry(pmde);
>   				if (!is_migration_entry(entry) ||
>   				    !check_pmd(swp_offset_pfn(entry), pvmw))
>   					return not_found(pvmw);

Why this change? Looks unrelated.

> @@ -277,6 +276,15 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>   			 * cannot return prematurely, while zap_huge_pmd() has
>   			 * cleared *pmd but not decremented compound_mapcount().

Reminder to self: cleanup compound_mapcount() leftovers

>   			 */
> +			swp_entry_t entry;
> +
> +			entry = pmd_to_swp_entry(pmde);

swp_entry_t entry = pmd_to_swp_entry(pmde);

> +
> +			if (is_device_private_entry(entry)) {
> +				pvmw->ptl = pmd_lock(mm, pvmw->pmd);
> +				return true;
> +			}
> +
>   			if ((pvmw->flags & PVMW_SYNC) &&
>   			    thp_vma_suitable_order(vma, pvmw->address,
>   						   PMD_ORDER) &&
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 236ceff5b276..6de1baf7a4f1 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1063,8 +1063,10 @@ static int page_vma_mkclean_one(struct page_vma_mapped_walk *pvmw)
>   		} else {
>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>   			pmd_t *pmd = pvmw->pmd;
> -			pmd_t entry;
> +			pmd_t entry = pmdp_get(pmd);
>   
> +			if (!pmd_present(entry))
> +				continue;
>   			if (!pmd_dirty(*pmd) && !pmd_write(*pmd))
>   				continue;
>   

If you just did a pmdp_get() you should use it in these functions as 
well. If not (cleanup later), do a straight *pmd like the others.



Apart from that nothing jumped at me.

-- 
Cheers

David / dhildenb

On 9/11/25 22:04, David Hildenbrand wrote:
> On 08.09.25 02:04, Balbir Singh wrote:
> 
> subject:
> 
> "mm/rmap: rmap and migration support for device-private PMD entries"
> 
> 
>> Add device-private THP support to reverse mapping infrastructure,
>> enabling proper handling during migration and walk operations.
>>
>> The key changes are:
>> - add_migration_pmd()/remove_migration_pmd(): Handle device-private
>>    entries during folio migration and splitting
>> - page_vma_mapped_walk(): Recognize device-private THP entries during
>>    VMA traversal operations
>>
>> This change supports folio splitting and migration operations on
>> device-private entries.
>>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Zi Yan <ziy@nvidia.com>
>> Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
>> Cc: Rakie Kim <rakie.kim@sk.com>
>> Cc: Byungchul Park <byungchul@sk.com>
>> Cc: Gregory Price <gourry@gourry.net>
>> Cc: Ying Huang <ying.huang@linux.alibaba.com>
>> Cc: Alistair Popple <apopple@nvidia.com>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
>> Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
>> Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
>> Cc: Nico Pache <npache@redhat.com>
>> Cc: Ryan Roberts <ryan.roberts@arm.com>
>> Cc: Dev Jain <dev.jain@arm.com>
>> Cc: Barry Song <baohua@kernel.org>
>> Cc: Lyude Paul <lyude@redhat.com>
>> Cc: Danilo Krummrich <dakr@kernel.org>
>> Cc: David Airlie <airlied@gmail.com>
>> Cc: Simona Vetter <simona@ffwll.ch>
>> Cc: Ralph Campbell <rcampbell@nvidia.com>
>> Cc: Mika Penttilä <mpenttil@redhat.com>
>> Cc: Matthew Brost <matthew.brost@intel.com>
>> Cc: Francois Dugast <francois.dugast@intel.com>
>>
>> Signed-off-by: Balbir Singh <balbirs@nvidia.com>
>> ---
> 
> [...]
> 
> 
>> +++ b/mm/page_vma_mapped.c
>> @@ -250,12 +250,11 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>>               pvmw->ptl = pmd_lock(mm, pvmw->pmd);
>>               pmde = *pvmw->pmd;
>>               if (!pmd_present(pmde)) {
>> -                swp_entry_t entry;
>> +                swp_entry_t entry = pmd_to_swp_entry(pmde);
>>                     if (!thp_migration_supported() ||
>>                       !(pvmw->flags & PVMW_MIGRATION))
>>                       return not_found(pvmw);
>> -                entry = pmd_to_swp_entry(pmde);
>>                   if (!is_migration_entry(entry) ||
>>                       !check_pmd(swp_offset_pfn(entry), pvmw))
>>                       return not_found(pvmw);
> 
> Why this change? Looks unrelated.
> 

I fixed up and removed the new flag I introduced in v3. Will fix/undo


>> @@ -277,6 +276,15 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>>                * cannot return prematurely, while zap_huge_pmd() has
>>                * cleared *pmd but not decremented compound_mapcount().
> 
> Reminder to self: cleanup compound_mapcount() leftovers
> 
>>                */
>> +            swp_entry_t entry;
>> +
>> +            entry = pmd_to_swp_entry(pmde);
> 
> swp_entry_t entry = pmd_to_swp_entry(pmde);
> 

Ack

>> +
>> +            if (is_device_private_entry(entry)) {
>> +                pvmw->ptl = pmd_lock(mm, pvmw->pmd);
>> +                return true;
>> +            }
>> +
>>               if ((pvmw->flags & PVMW_SYNC) &&
>>                   thp_vma_suitable_order(vma, pvmw->address,
>>                              PMD_ORDER) &&
>> diff --git a/mm/rmap.c b/mm/rmap.c
>> index 236ceff5b276..6de1baf7a4f1 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -1063,8 +1063,10 @@ static int page_vma_mkclean_one(struct page_vma_mapped_walk *pvmw)
>>           } else {
>>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>               pmd_t *pmd = pvmw->pmd;
>> -            pmd_t entry;
>> +            pmd_t entry = pmdp_get(pmd);
>>   +            if (!pmd_present(entry))
>> +                continue;
>>               if (!pmd_dirty(*pmd) && !pmd_write(*pmd))
>>                   continue;
>>   
> 
> If you just did a pmdp_get() you should use it in these functions as well. If not (cleanup later), do a straight *pmd like the others.
> 
> 

Ack

> 
> Apart from that nothing jumped at me.
> 

Thanks for the review,
Balbir