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[PATCH v1 19/29] mm: stop storing migration_ops in page->mapping

David Hildenbrand posted 29 patches 7 months, 1 week ago
There is a newer version of this series
[PATCH v1 19/29] mm: stop storing migration_ops in page->mapping
Posted by David Hildenbrand 7 months, 1 week ago 
... instead, look them up statically based on the page type. Maybe in the
future we want a registration interface? At least for now, it can be
easily handled using the two page types that actually support page
migration.

The remaining usage of page->mapping is to flag such pages as actually
being movable (having movable_ops), which we will change next.

Reviewed-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 include/linux/balloon_compaction.h |  2 +-
 include/linux/migrate.h            | 14 ++------------
 include/linux/zsmalloc.h           |  2 ++
 mm/balloon_compaction.c            |  1 -
 mm/compaction.c                    |  5 ++---
 mm/migrate.c                       | 23 +++++++++++++++++++++++
 mm/zpdesc.h                        |  5 ++---
 mm/zsmalloc.c                      |  8 +++-----
 8 files changed, 35 insertions(+), 25 deletions(-)

diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
index 9bce8e9f5018c..a8a1706cc56f3 100644
--- a/include/linux/balloon_compaction.h
+++ b/include/linux/balloon_compaction.h
@@ -92,7 +92,7 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
 				       struct page *page)
 {
 	__SetPageOffline(page);
-	__SetPageMovable(page, &balloon_mops);
+	__SetPageMovable(page);
 	set_page_private(page, (unsigned long)balloon);
 	list_add(&page->lru, &balloon->pages);
 }
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index e04035f70e36f..6aece3f3c8be8 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -104,23 +104,13 @@ static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
 #endif /* CONFIG_MIGRATION */
 
 #ifdef CONFIG_COMPACTION
-void __SetPageMovable(struct page *page, const struct movable_operations *ops);
+void __SetPageMovable(struct page *page);
 #else
-static inline void __SetPageMovable(struct page *page,
-		const struct movable_operations *ops)
+static inline void __SetPageMovable(struct page *page)
 {
 }
 #endif
 
-static inline
-const struct movable_operations *page_movable_ops(struct page *page)
-{
-	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
-
-	return (const struct movable_operations *)
-		((unsigned long)page->mapping - PAGE_MAPPING_MOVABLE);
-}
-
 #ifdef CONFIG_NUMA_BALANCING
 int migrate_misplaced_folio_prepare(struct folio *folio,
 		struct vm_area_struct *vma, int node);
diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h
index 13e9cc5490f71..f3ccff2d966cd 100644
--- a/include/linux/zsmalloc.h
+++ b/include/linux/zsmalloc.h
@@ -46,4 +46,6 @@ void zs_obj_read_end(struct zs_pool *pool, unsigned long handle,
 void zs_obj_write(struct zs_pool *pool, unsigned long handle,
 		  void *handle_mem, size_t mem_len);
 
+extern const struct movable_operations zsmalloc_mops;
+
 #endif
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index e4f1a122d786b..2a4a649805c11 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -253,6 +253,5 @@ const struct movable_operations balloon_mops = {
 	.isolate_page = balloon_page_isolate,
 	.putback_page = balloon_page_putback,
 };
-EXPORT_SYMBOL_GPL(balloon_mops);
 
 #endif /* CONFIG_BALLOON_COMPACTION */
diff --git a/mm/compaction.c b/mm/compaction.c
index 41fd6a1fe9a33..348eb754cb227 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -114,11 +114,10 @@ static unsigned long release_free_list(struct list_head *freepages)
 }
 
 #ifdef CONFIG_COMPACTION
-void __SetPageMovable(struct page *page, const struct movable_operations *mops)
+void __SetPageMovable(struct page *page)
 {
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
-	VM_BUG_ON_PAGE((unsigned long)mops & PAGE_MAPPING_MOVABLE, page);
-	page->mapping = (void *)((unsigned long)mops | PAGE_MAPPING_MOVABLE);
+	page->mapping = (void *)(PAGE_MAPPING_MOVABLE);
 }
 EXPORT_SYMBOL(__SetPageMovable);
 
diff --git a/mm/migrate.c b/mm/migrate.c
index 15d3c1031530c..c6c9998014ec8 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -43,6 +43,8 @@
 #include <linux/sched/sysctl.h>
 #include <linux/memory-tiers.h>
 #include <linux/pagewalk.h>
+#include <linux/balloon_compaction.h>
+#include <linux/zsmalloc.h>
 
 #include <asm/tlbflush.h>
 
@@ -51,6 +53,27 @@
 #include "internal.h"
 #include "swap.h"
 
+static const struct movable_operations *page_movable_ops(struct page *page)
+{
+	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
+
+	/*
+	 * If we enable page migration for a page of a certain type by marking
+	 * it as movable, the page type must be sticky until the page gets freed
+	 * back to the buddy.
+	 */
+#ifdef CONFIG_BALLOON_COMPACTION
+	if (PageOffline(page))
+		/* Only balloon compaction sets PageOffline pages movable. */
+		return &balloon_mops;
+#endif /* CONFIG_BALLOON_COMPACTION */
+#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION)
+	if (PageZsmalloc(page))
+		return &zsmalloc_mops;
+#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */
+	return NULL;
+}
+
 /**
  * isolate_movable_ops_page - isolate a movable_ops page for migration
  * @page: The page.
diff --git a/mm/zpdesc.h b/mm/zpdesc.h
index 5763f36039736..6855d9e2732d8 100644
--- a/mm/zpdesc.h
+++ b/mm/zpdesc.h
@@ -152,10 +152,9 @@ static inline struct zpdesc *pfn_zpdesc(unsigned long pfn)
 	return page_zpdesc(pfn_to_page(pfn));
 }
 
-static inline void __zpdesc_set_movable(struct zpdesc *zpdesc,
-					const struct movable_operations *mops)
+static inline void __zpdesc_set_movable(struct zpdesc *zpdesc)
 {
-	__SetPageMovable(zpdesc_page(zpdesc), mops);
+	__SetPageMovable(zpdesc_page(zpdesc));
 }
 
 static inline void __zpdesc_set_zsmalloc(struct zpdesc *zpdesc)
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 72c2b7562c511..7192196b9421d 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1684,8 +1684,6 @@ static void lock_zspage(struct zspage *zspage)
 
 #ifdef CONFIG_COMPACTION
 
-static const struct movable_operations zsmalloc_mops;
-
 static void replace_sub_page(struct size_class *class, struct zspage *zspage,
 				struct zpdesc *newzpdesc, struct zpdesc *oldzpdesc)
 {
@@ -1708,7 +1706,7 @@ static void replace_sub_page(struct size_class *class, struct zspage *zspage,
 	set_first_obj_offset(newzpdesc, first_obj_offset);
 	if (unlikely(ZsHugePage(zspage)))
 		newzpdesc->handle = oldzpdesc->handle;
-	__zpdesc_set_movable(newzpdesc, &zsmalloc_mops);
+	__zpdesc_set_movable(newzpdesc);
 }
 
 static bool zs_page_isolate(struct page *page, isolate_mode_t mode)
@@ -1815,7 +1813,7 @@ static void zs_page_putback(struct page *page)
 {
 }
 
-static const struct movable_operations zsmalloc_mops = {
+const struct movable_operations zsmalloc_mops = {
 	.isolate_page = zs_page_isolate,
 	.migrate_page = zs_page_migrate,
 	.putback_page = zs_page_putback,
@@ -1878,7 +1876,7 @@ static void SetZsPageMovable(struct zs_pool *pool, struct zspage *zspage)
 
 	do {
 		WARN_ON(!zpdesc_trylock(zpdesc));
-		__zpdesc_set_movable(zpdesc, &zsmalloc_mops);
+		__zpdesc_set_movable(zpdesc);
 		zpdesc_unlock(zpdesc);
 	} while ((zpdesc = get_next_zpdesc(zpdesc)) != NULL);
 }
-- 
2.49.0
Re: [PATCH v1 19/29] mm: stop storing migration_ops in page->mapping
Posted by Harry Yoo 7 months, 1 week ago 
On Mon, Jun 30, 2025 at 03:00:00PM +0200, David Hildenbrand wrote:
> ... instead, look them up statically based on the page type. Maybe in the
> future we want a registration interface? At least for now, it can be
> easily handled using the two page types that actually support page
> migration.
> 
> The remaining usage of page->mapping is to flag such pages as actually
> being movable (having movable_ops), which we will change next.
> 
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---

> +static const struct movable_operations *page_movable_ops(struct page *page)
> +{
> +	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
> +
> +	/*
> +	 * If we enable page migration for a page of a certain type by marking
> +	 * it as movable, the page type must be sticky until the page gets freed
> +	 * back to the buddy.
> +	 */
> +#ifdef CONFIG_BALLOON_COMPACTION
> +	if (PageOffline(page))
> +		/* Only balloon compaction sets PageOffline pages movable. */
> +		return &balloon_mops;
> +#endif /* CONFIG_BALLOON_COMPACTION */
> +#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION)
> +	if (PageZsmalloc(page))
> +		return &zsmalloc_mops;
> +#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */

What happens if:
  CONFIG_ZSMALLOC=y
  CONFIG_TRANSPARENT_HUGEPAGE=n
  CONFIG_COMPACTION=n
  CONFIG_MIGRATION=y

?

> +	return NULL;
> +}
> +
>  /**
>   * isolate_movable_ops_page - isolate a movable_ops page for migration
>   * @page: The page.

Otherwise LGTM.

-- 
Cheers,
Harry / Hyeonggon
Re: [PATCH v1 19/29] mm: stop storing migration_ops in page->mapping
Posted by David Hildenbrand 7 months, 1 week ago 
On 02.07.25 12:34, Harry Yoo wrote:
> On Mon, Jun 30, 2025 at 03:00:00PM +0200, David Hildenbrand wrote:
>> ... instead, look them up statically based on the page type. Maybe in the
>> future we want a registration interface? At least for now, it can be
>> easily handled using the two page types that actually support page
>> migration.
>>
>> The remaining usage of page->mapping is to flag such pages as actually
>> being movable (having movable_ops), which we will change next.
>>
>> Reviewed-by: Zi Yan <ziy@nvidia.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
> 
>> +static const struct movable_operations *page_movable_ops(struct page *page)
>> +{
>> +	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
>> +
>> +	/*
>> +	 * If we enable page migration for a page of a certain type by marking
>> +	 * it as movable, the page type must be sticky until the page gets freed
>> +	 * back to the buddy.
>> +	 */
>> +#ifdef CONFIG_BALLOON_COMPACTION
>> +	if (PageOffline(page))
>> +		/* Only balloon compaction sets PageOffline pages movable. */
>> +		return &balloon_mops;
>> +#endif /* CONFIG_BALLOON_COMPACTION */
>> +#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION)
>> +	if (PageZsmalloc(page))
>> +		return &zsmalloc_mops;
>> +#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */
> 
> What happens if:
>    CONFIG_ZSMALLOC=y
>    CONFIG_TRANSPARENT_HUGEPAGE=n
>    CONFIG_COMPACTION=n
>    CONFIG_MIGRATION=y

Pages are never allocated from ZONE_MOVABLE/CMA and are not marked as 
having movable_ops, so we never end up in this function. See how 
zsmalloc.c deals with CONFIG_COMPACTION, especially how 
SetZsPageMovable() is a NOP without it.

As a side note, both should probably be moved from COMPACTION to 
MIGRATION. Although probably in practice, anybody enabling 
CONFIG_MIGRATION likely also enables CONFIG_COMPACTION.

-- 
Cheers,

David / dhildenb
Re: [PATCH v1 19/29] mm: stop storing migration_ops in page->mapping
Posted by Harry Yoo 7 months, 1 week ago 
On Wed, Jul 02, 2025 at 01:04:05PM +0200, David Hildenbrand wrote:
> On 02.07.25 12:34, Harry Yoo wrote:
> > On Mon, Jun 30, 2025 at 03:00:00PM +0200, David Hildenbrand wrote:
> > > ... instead, look them up statically based on the page type. Maybe in the
> > > future we want a registration interface? At least for now, it can be
> > > easily handled using the two page types that actually support page
> > > migration.
> > > 
> > > The remaining usage of page->mapping is to flag such pages as actually
> > > being movable (having movable_ops), which we will change next.
> > > 
> > > Reviewed-by: Zi Yan <ziy@nvidia.com>
> > > Signed-off-by: David Hildenbrand <david@redhat.com>
> > > ---
> > 
> > > +static const struct movable_operations *page_movable_ops(struct page *page)
> > > +{
> > > +	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
> > > +
> > > +	/*
> > > +	 * If we enable page migration for a page of a certain type by marking
> > > +	 * it as movable, the page type must be sticky until the page gets freed
> > > +	 * back to the buddy.
> > > +	 */
> > > +#ifdef CONFIG_BALLOON_COMPACTION
> > > +	if (PageOffline(page))
> > > +		/* Only balloon compaction sets PageOffline pages movable. */
> > > +		return &balloon_mops;
> > > +#endif /* CONFIG_BALLOON_COMPACTION */
> > > +#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION)
> > > +	if (PageZsmalloc(page))
> > > +		return &zsmalloc_mops;
> > > +#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */
> > 
> > What happens if:
> >    CONFIG_ZSMALLOC=y
> >    CONFIG_TRANSPARENT_HUGEPAGE=n
> >    CONFIG_COMPACTION=n
> >    CONFIG_MIGRATION=y
> 
> Pages are never allocated from ZONE_MOVABLE/CMA and

I don't understand how that's true, neither zram nor zsmalloc clears
__GFP_MOVABLE when CONFIG_COMPACTION=n?

...Or perhaps I'm still missing some pieces ;)
 
> are not marked as having movable_ops, so we never end up in this function.

Right.

> See how zsmalloc.c deals with CONFIG_COMPACTION, especially how
> SetZsPageMovable() is a NOP without it.

Right.

Now I see what I was missing in the previous reply.
Thanks!

Please feel free to add:

Reviewed-by: Harry Yoo <harry.yoo@oracle.com>

-- 
Cheers,
Harry / Hyeonggon
Re: [PATCH v1 19/29] mm: stop storing migration_ops in page->mapping
Posted by David Hildenbrand 7 months, 1 week ago 
On 02.07.25 13:43, Harry Yoo wrote:
> On Wed, Jul 02, 2025 at 01:04:05PM +0200, David Hildenbrand wrote:
>> On 02.07.25 12:34, Harry Yoo wrote:
>>> On Mon, Jun 30, 2025 at 03:00:00PM +0200, David Hildenbrand wrote:
>>>> ... instead, look them up statically based on the page type. Maybe in the
>>>> future we want a registration interface? At least for now, it can be
>>>> easily handled using the two page types that actually support page
>>>> migration.
>>>>
>>>> The remaining usage of page->mapping is to flag such pages as actually
>>>> being movable (having movable_ops), which we will change next.
>>>>
>>>> Reviewed-by: Zi Yan <ziy@nvidia.com>
>>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>>> ---
>>>
>>>> +static const struct movable_operations *page_movable_ops(struct page *page)
>>>> +{
>>>> +	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
>>>> +
>>>> +	/*
>>>> +	 * If we enable page migration for a page of a certain type by marking
>>>> +	 * it as movable, the page type must be sticky until the page gets freed
>>>> +	 * back to the buddy.
>>>> +	 */
>>>> +#ifdef CONFIG_BALLOON_COMPACTION
>>>> +	if (PageOffline(page))
>>>> +		/* Only balloon compaction sets PageOffline pages movable. */
>>>> +		return &balloon_mops;
>>>> +#endif /* CONFIG_BALLOON_COMPACTION */
>>>> +#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION)
>>>> +	if (PageZsmalloc(page))
>>>> +		return &zsmalloc_mops;
>>>> +#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */
>>>
>>> What happens if:
>>>     CONFIG_ZSMALLOC=y
>>>     CONFIG_TRANSPARENT_HUGEPAGE=n
>>>     CONFIG_COMPACTION=n
>>>     CONFIG_MIGRATION=y
>>
>> Pages are never allocated from ZONE_MOVABLE/CMA and
> 
> I don't understand how that's true, neither zram nor zsmalloc clears
> __GFP_MOVABLE when CONFIG_COMPACTION=n?
> 
> ...Or perhaps I'm still missing some pieces ;)

You might have found a bug in zsmalloc then :) Without support for compaction, we
must clear __GFP_MOVABLE in alloc_zpdesc() I assume.

Do you have the capacity to look into that and send a fix if really broken?

In balloon compaction code we properly handle that.

>   
>> are not marked as having movable_ops, so we never end up in this function.
> 
> Right.
> 
>> See how zsmalloc.c deals with CONFIG_COMPACTION, especially how
>> SetZsPageMovable() is a NOP without it.
> 
> Right.
> 
> Now I see what I was missing in the previous reply.
> Thanks!
> 
> Please feel free to add:
> 
> Reviewed-by: Harry Yoo <harry.yoo@oracle.com>

Thanks!

-- 
Cheers,

David / dhildenb
Re: [PATCH v1 19/29] mm: stop storing migration_ops in page->mapping
Posted by Harry Yoo 7 months, 1 week ago 
On Wed, Jul 02, 2025 at 01:51:52PM +0200, David Hildenbrand wrote:
> On 02.07.25 13:43, Harry Yoo wrote:
> > On Wed, Jul 02, 2025 at 01:04:05PM +0200, David Hildenbrand wrote:
> > > On 02.07.25 12:34, Harry Yoo wrote:
> > > > On Mon, Jun 30, 2025 at 03:00:00PM +0200, David Hildenbrand wrote:
> > > > > ... instead, look them up statically based on the page type. Maybe in the
> > > > > future we want a registration interface? At least for now, it can be
> > > > > easily handled using the two page types that actually support page
> > > > > migration.
> > > > > 
> > > > > The remaining usage of page->mapping is to flag such pages as actually
> > > > > being movable (having movable_ops), which we will change next.
> > > > > 
> > > > > Reviewed-by: Zi Yan <ziy@nvidia.com>
> > > > > Signed-off-by: David Hildenbrand <david@redhat.com>
> > > > > ---
> > > > 
> > > > > +static const struct movable_operations *page_movable_ops(struct page *page)
> > > > > +{
> > > > > +	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
> > > > > +
> > > > > +	/*
> > > > > +	 * If we enable page migration for a page of a certain type by marking
> > > > > +	 * it as movable, the page type must be sticky until the page gets freed
> > > > > +	 * back to the buddy.
> > > > > +	 */
> > > > > +#ifdef CONFIG_BALLOON_COMPACTION
> > > > > +	if (PageOffline(page))
> > > > > +		/* Only balloon compaction sets PageOffline pages movable. */
> > > > > +		return &balloon_mops;
> > > > > +#endif /* CONFIG_BALLOON_COMPACTION */
> > > > > +#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION)
> > > > > +	if (PageZsmalloc(page))
> > > > > +		return &zsmalloc_mops;
> > > > > +#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */
> > > > 
> > > > What happens if:
> > > >     CONFIG_ZSMALLOC=y
> > > >     CONFIG_TRANSPARENT_HUGEPAGE=n
> > > >     CONFIG_COMPACTION=n
> > > >     CONFIG_MIGRATION=y
> > > 
> > > Pages are never allocated from ZONE_MOVABLE/CMA and
> > 
> > I don't understand how that's true, neither zram nor zsmalloc clears
> > __GFP_MOVABLE when CONFIG_COMPACTION=n?
> > 
> > ...Or perhaps I'm still missing some pieces ;)
> 
> You might have found a bug in zsmalloc then :) Without support for compaction, we
> must clear __GFP_MOVABLE in alloc_zpdesc() I assume.
> 
> Do you have the capacity to look into that and send a fix if really broken?

I'll add that to somehwere in my TODO list :)

1) confirming if it's really broken and
2) fixing it if so.
 
> In balloon compaction code we properly handle that.

-- 
Cheers,
Harry / Hyeonggon
Re: [PATCH v1 19/29] mm: stop storing migration_ops in page->mapping
Posted by Lorenzo Stoakes 7 months, 1 week ago 
On Mon, Jun 30, 2025 at 03:00:00PM +0200, David Hildenbrand wrote:
> ... instead, look them up statically based on the page type. Maybe in the
> future we want a registration interface? At least for now, it can be
> easily handled using the two page types that actually support page
> migration.
>
> The remaining usage of page->mapping is to flag such pages as actually
> being movable (having movable_ops), which we will change next.
>
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

See comment below, this feels iffy in the long run but ok as an interim measure.

So:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
>  include/linux/balloon_compaction.h |  2 +-
>  include/linux/migrate.h            | 14 ++------------
>  include/linux/zsmalloc.h           |  2 ++
>  mm/balloon_compaction.c            |  1 -
>  mm/compaction.c                    |  5 ++---
>  mm/migrate.c                       | 23 +++++++++++++++++++++++
>  mm/zpdesc.h                        |  5 ++---
>  mm/zsmalloc.c                      |  8 +++-----
>  8 files changed, 35 insertions(+), 25 deletions(-)
>
> diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
> index 9bce8e9f5018c..a8a1706cc56f3 100644
> --- a/include/linux/balloon_compaction.h
> +++ b/include/linux/balloon_compaction.h
> @@ -92,7 +92,7 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
>  				       struct page *page)
>  {
>  	__SetPageOffline(page);
> -	__SetPageMovable(page, &balloon_mops);
> +	__SetPageMovable(page);
>  	set_page_private(page, (unsigned long)balloon);
>  	list_add(&page->lru, &balloon->pages);
>  }
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index e04035f70e36f..6aece3f3c8be8 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -104,23 +104,13 @@ static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
>  #endif /* CONFIG_MIGRATION */
>
>  #ifdef CONFIG_COMPACTION
> -void __SetPageMovable(struct page *page, const struct movable_operations *ops);
> +void __SetPageMovable(struct page *page);
>  #else
> -static inline void __SetPageMovable(struct page *page,
> -		const struct movable_operations *ops)
> +static inline void __SetPageMovable(struct page *page)
>  {
>  }
>  #endif
>
> -static inline
> -const struct movable_operations *page_movable_ops(struct page *page)
> -{
> -	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
> -
> -	return (const struct movable_operations *)
> -		((unsigned long)page->mapping - PAGE_MAPPING_MOVABLE);
> -}
> -
>  #ifdef CONFIG_NUMA_BALANCING
>  int migrate_misplaced_folio_prepare(struct folio *folio,
>  		struct vm_area_struct *vma, int node);
> diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h
> index 13e9cc5490f71..f3ccff2d966cd 100644
> --- a/include/linux/zsmalloc.h
> +++ b/include/linux/zsmalloc.h
> @@ -46,4 +46,6 @@ void zs_obj_read_end(struct zs_pool *pool, unsigned long handle,
>  void zs_obj_write(struct zs_pool *pool, unsigned long handle,
>  		  void *handle_mem, size_t mem_len);
>
> +extern const struct movable_operations zsmalloc_mops;
> +
>  #endif
> diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
> index e4f1a122d786b..2a4a649805c11 100644
> --- a/mm/balloon_compaction.c
> +++ b/mm/balloon_compaction.c
> @@ -253,6 +253,5 @@ const struct movable_operations balloon_mops = {
>  	.isolate_page = balloon_page_isolate,
>  	.putback_page = balloon_page_putback,
>  };
> -EXPORT_SYMBOL_GPL(balloon_mops);
>
>  #endif /* CONFIG_BALLOON_COMPACTION */
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 41fd6a1fe9a33..348eb754cb227 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -114,11 +114,10 @@ static unsigned long release_free_list(struct list_head *freepages)
>  }
>
>  #ifdef CONFIG_COMPACTION
> -void __SetPageMovable(struct page *page, const struct movable_operations *mops)
> +void __SetPageMovable(struct page *page)
>  {
>  	VM_BUG_ON_PAGE(!PageLocked(page), page);
> -	VM_BUG_ON_PAGE((unsigned long)mops & PAGE_MAPPING_MOVABLE, page);
> -	page->mapping = (void *)((unsigned long)mops | PAGE_MAPPING_MOVABLE);
> +	page->mapping = (void *)(PAGE_MAPPING_MOVABLE);
>  }
>  EXPORT_SYMBOL(__SetPageMovable);
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 15d3c1031530c..c6c9998014ec8 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -43,6 +43,8 @@
>  #include <linux/sched/sysctl.h>
>  #include <linux/memory-tiers.h>
>  #include <linux/pagewalk.h>
> +#include <linux/balloon_compaction.h>
> +#include <linux/zsmalloc.h>
>
>  #include <asm/tlbflush.h>
>
> @@ -51,6 +53,27 @@
>  #include "internal.h"
>  #include "swap.h"
>
> +static const struct movable_operations *page_movable_ops(struct page *page)
> +{
> +	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
> +
> +	/*
> +	 * If we enable page migration for a page of a certain type by marking
> +	 * it as movable, the page type must be sticky until the page gets freed
> +	 * back to the buddy.
> +	 */

Ah now this makes more sense...

> +#ifdef CONFIG_BALLOON_COMPACTION
> +	if (PageOffline(page))
> +		/* Only balloon compaction sets PageOffline pages movable. */
> +		return &balloon_mops;

So it's certain that if we try to invoke movable ops, and it's the balloon
compaction case, the page will be offline?

> +#endif /* CONFIG_BALLOON_COMPACTION */
> +#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION)
> +	if (PageZsmalloc(page))

And same question only for ZS malloc.

> +		return &zsmalloc_mops;
> +#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */
> +	return NULL;
> +}

This is kind of sketchy as it's baking in assumptions implicitly, so I hope we
can find an improved way of doing this later, even if it's about providing
e.g. is_ballon_movable_ops_page() and is_zsmalloc_movable_ops_page() predicates
that abstract this code + placing them in the relevant code so it's at least
obvious to people working on this stuff that this needs to be considered.

But ok as a means of getting away from having to have the hook object encoded.

> +
>  /**
>   * isolate_movable_ops_page - isolate a movable_ops page for migration
>   * @page: The page.
> diff --git a/mm/zpdesc.h b/mm/zpdesc.h
> index 5763f36039736..6855d9e2732d8 100644
> --- a/mm/zpdesc.h
> +++ b/mm/zpdesc.h
> @@ -152,10 +152,9 @@ static inline struct zpdesc *pfn_zpdesc(unsigned long pfn)
>  	return page_zpdesc(pfn_to_page(pfn));
>  }
>
> -static inline void __zpdesc_set_movable(struct zpdesc *zpdesc,
> -					const struct movable_operations *mops)
> +static inline void __zpdesc_set_movable(struct zpdesc *zpdesc)
>  {
> -	__SetPageMovable(zpdesc_page(zpdesc), mops);
> +	__SetPageMovable(zpdesc_page(zpdesc));
>  }
>
>  static inline void __zpdesc_set_zsmalloc(struct zpdesc *zpdesc)
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 72c2b7562c511..7192196b9421d 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1684,8 +1684,6 @@ static void lock_zspage(struct zspage *zspage)
>
>  #ifdef CONFIG_COMPACTION
>
> -static const struct movable_operations zsmalloc_mops;
> -
>  static void replace_sub_page(struct size_class *class, struct zspage *zspage,
>  				struct zpdesc *newzpdesc, struct zpdesc *oldzpdesc)
>  {
> @@ -1708,7 +1706,7 @@ static void replace_sub_page(struct size_class *class, struct zspage *zspage,
>  	set_first_obj_offset(newzpdesc, first_obj_offset);
>  	if (unlikely(ZsHugePage(zspage)))
>  		newzpdesc->handle = oldzpdesc->handle;
> -	__zpdesc_set_movable(newzpdesc, &zsmalloc_mops);
> +	__zpdesc_set_movable(newzpdesc);
>  }
>
>  static bool zs_page_isolate(struct page *page, isolate_mode_t mode)
> @@ -1815,7 +1813,7 @@ static void zs_page_putback(struct page *page)
>  {
>  }
>
> -static const struct movable_operations zsmalloc_mops = {
> +const struct movable_operations zsmalloc_mops = {
>  	.isolate_page = zs_page_isolate,
>  	.migrate_page = zs_page_migrate,
>  	.putback_page = zs_page_putback,
> @@ -1878,7 +1876,7 @@ static void SetZsPageMovable(struct zs_pool *pool, struct zspage *zspage)
>
>  	do {
>  		WARN_ON(!zpdesc_trylock(zpdesc));
> -		__zpdesc_set_movable(zpdesc, &zsmalloc_mops);
> +		__zpdesc_set_movable(zpdesc);
>  		zpdesc_unlock(zpdesc);
>  	} while ((zpdesc = get_next_zpdesc(zpdesc)) != NULL);
>  }
> --
> 2.49.0
>
Re: [PATCH v1 19/29] mm: stop storing migration_ops in page->mapping
Posted by David Hildenbrand 7 months, 1 week ago 
On 01.07.25 14:12, Lorenzo Stoakes wrote:
> On Mon, Jun 30, 2025 at 03:00:00PM +0200, David Hildenbrand wrote:
>> ... instead, look them up statically based on the page type. Maybe in the
>> future we want a registration interface? At least for now, it can be
>> easily handled using the two page types that actually support page
>> migration.
>>
>> The remaining usage of page->mapping is to flag such pages as actually
>> being movable (having movable_ops), which we will change next.
>>
>> Reviewed-by: Zi Yan <ziy@nvidia.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
> 
> See comment below, this feels iffy in the long run but ok as an interim measure.
> 
> So:
> 
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> 
>> ---
>>   include/linux/balloon_compaction.h |  2 +-
>>   include/linux/migrate.h            | 14 ++------------
>>   include/linux/zsmalloc.h           |  2 ++
>>   mm/balloon_compaction.c            |  1 -
>>   mm/compaction.c                    |  5 ++---
>>   mm/migrate.c                       | 23 +++++++++++++++++++++++
>>   mm/zpdesc.h                        |  5 ++---
>>   mm/zsmalloc.c                      |  8 +++-----
>>   8 files changed, 35 insertions(+), 25 deletions(-)
>>
>> diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
>> index 9bce8e9f5018c..a8a1706cc56f3 100644
>> --- a/include/linux/balloon_compaction.h
>> +++ b/include/linux/balloon_compaction.h
>> @@ -92,7 +92,7 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
>>   				       struct page *page)
>>   {
>>   	__SetPageOffline(page);
>> -	__SetPageMovable(page, &balloon_mops);
>> +	__SetPageMovable(page);
>>   	set_page_private(page, (unsigned long)balloon);
>>   	list_add(&page->lru, &balloon->pages);
>>   }
>> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
>> index e04035f70e36f..6aece3f3c8be8 100644
>> --- a/include/linux/migrate.h
>> +++ b/include/linux/migrate.h
>> @@ -104,23 +104,13 @@ static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
>>   #endif /* CONFIG_MIGRATION */
>>
>>   #ifdef CONFIG_COMPACTION
>> -void __SetPageMovable(struct page *page, const struct movable_operations *ops);
>> +void __SetPageMovable(struct page *page);
>>   #else
>> -static inline void __SetPageMovable(struct page *page,
>> -		const struct movable_operations *ops)
>> +static inline void __SetPageMovable(struct page *page)
>>   {
>>   }
>>   #endif
>>
>> -static inline
>> -const struct movable_operations *page_movable_ops(struct page *page)
>> -{
>> -	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
>> -
>> -	return (const struct movable_operations *)
>> -		((unsigned long)page->mapping - PAGE_MAPPING_MOVABLE);
>> -}
>> -
>>   #ifdef CONFIG_NUMA_BALANCING
>>   int migrate_misplaced_folio_prepare(struct folio *folio,
>>   		struct vm_area_struct *vma, int node);
>> diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h
>> index 13e9cc5490f71..f3ccff2d966cd 100644
>> --- a/include/linux/zsmalloc.h
>> +++ b/include/linux/zsmalloc.h
>> @@ -46,4 +46,6 @@ void zs_obj_read_end(struct zs_pool *pool, unsigned long handle,
>>   void zs_obj_write(struct zs_pool *pool, unsigned long handle,
>>   		  void *handle_mem, size_t mem_len);
>>
>> +extern const struct movable_operations zsmalloc_mops;
>> +
>>   #endif
>> diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
>> index e4f1a122d786b..2a4a649805c11 100644
>> --- a/mm/balloon_compaction.c
>> +++ b/mm/balloon_compaction.c
>> @@ -253,6 +253,5 @@ const struct movable_operations balloon_mops = {
>>   	.isolate_page = balloon_page_isolate,
>>   	.putback_page = balloon_page_putback,
>>   };
>> -EXPORT_SYMBOL_GPL(balloon_mops);
>>
>>   #endif /* CONFIG_BALLOON_COMPACTION */
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index 41fd6a1fe9a33..348eb754cb227 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -114,11 +114,10 @@ static unsigned long release_free_list(struct list_head *freepages)
>>   }
>>
>>   #ifdef CONFIG_COMPACTION
>> -void __SetPageMovable(struct page *page, const struct movable_operations *mops)
>> +void __SetPageMovable(struct page *page)
>>   {
>>   	VM_BUG_ON_PAGE(!PageLocked(page), page);
>> -	VM_BUG_ON_PAGE((unsigned long)mops & PAGE_MAPPING_MOVABLE, page);
>> -	page->mapping = (void *)((unsigned long)mops | PAGE_MAPPING_MOVABLE);
>> +	page->mapping = (void *)(PAGE_MAPPING_MOVABLE);
>>   }
>>   EXPORT_SYMBOL(__SetPageMovable);
>>
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 15d3c1031530c..c6c9998014ec8 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -43,6 +43,8 @@
>>   #include <linux/sched/sysctl.h>
>>   #include <linux/memory-tiers.h>
>>   #include <linux/pagewalk.h>
>> +#include <linux/balloon_compaction.h>
>> +#include <linux/zsmalloc.h>
>>
>>   #include <asm/tlbflush.h>
>>
>> @@ -51,6 +53,27 @@
>>   #include "internal.h"
>>   #include "swap.h"
>>
>> +static const struct movable_operations *page_movable_ops(struct page *page)
>> +{
>> +	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
>> +
>> +	/*
>> +	 * If we enable page migration for a page of a certain type by marking
>> +	 * it as movable, the page type must be sticky until the page gets freed
>> +	 * back to the buddy.
>> +	 */
> 
> Ah now this makes more sense...
> 
>> +#ifdef CONFIG_BALLOON_COMPACTION
>> +	if (PageOffline(page))
>> +		/* Only balloon compaction sets PageOffline pages movable. */
>> +		return &balloon_mops;
> 
> So it's certain that if we try to invoke movable ops, and it's the balloon
> compaction case, the page will be offline?

Yes. The page must be marked as having movable_ops by the user. The next 
patch reworks that as well.

A PageOffline page without movable_ops will never end up here 
(page_has_movable_ops() == false).

> 
>> +#endif /* CONFIG_BALLOON_COMPACTION */
>> +#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION)
>> +	if (PageZsmalloc(page))
> 
> And same question only for ZS malloc.

Same thing.

> 
>> +		return &zsmalloc_mops;
>> +#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */
>> +	return NULL;
>> +}
> 
> This is kind of sketchy as it's baking in assumptions implicitly, so I hope we
> can find an improved way of doing this later, even if it's about providing
> e.g. is_ballon_movable_ops_page() and is_zsmalloc_movable_ops_page() predicates
> that abstract this code + placing them in the relevant code so it's at least
> obvious to people working on this stuff that this needs to be considered.
> 
> But ok as a means of getting away from having to have the hook object encoded.

Yeah, not sure yet how to clean that up in the future. As I stated 
somewhere, maybe we just want a registration interface to handle a 
specific page type. But for handling the two known in-tree users, this 
should get us going.

Thanks!

-- 
Cheers,

David / dhildenb

Patchew 2.1-devel-b67e4c2

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