On 18.09.25 04:49, Zi Yan wrote:
On 16 Sep 2025, at 8:21, Balbir Singh wrote:
Add routines to support allocation of large order zone device folios
and helper functions for zone device folios, to check if a folio is
device private and helpers for setting zone device data.
When large folios are used, the existing page_free() callback in
pgmap is called when the folio is freed, this is true for both
PAGE_SIZE and higher order pages.
Zone device private large folios do not support deferred split and
scan like normal THP folios.
Signed-off-by: Balbir Singh <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Zi Yan <[email protected]>
Cc: Joshua Hahn <[email protected]>
Cc: Rakie Kim <[email protected]>
Cc: Byungchul Park <[email protected]>
Cc: Gregory Price <[email protected]>
Cc: Ying Huang <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Baolin Wang <[email protected]>
Cc: "Liam R. Howlett" <[email protected]>
Cc: Nico Pache <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Dev Jain <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Lyude Paul <[email protected]>
Cc: Danilo Krummrich <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Simona Vetter <[email protected]>
Cc: Ralph Campbell <[email protected]>
Cc: Mika Penttilä <[email protected]>
Cc: Matthew Brost <[email protected]>
Cc: Francois Dugast <[email protected]>
---
include/linux/memremap.h | 10 +++++++++-
mm/memremap.c | 34 +++++++++++++++++++++-------------
mm/rmap.c | 6 +++++-
3 files changed, 35 insertions(+), 15 deletions(-)
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index e5951ba12a28..9c20327c2be5 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -206,7 +206,7 @@ static inline bool is_fsdax_page(const struct page *page)
}
#ifdef CONFIG_ZONE_DEVICE
-void zone_device_page_init(struct page *page);
+void zone_device_folio_init(struct folio *folio, unsigned int order);
void *memremap_pages(struct dev_pagemap *pgmap, int nid);
void memunmap_pages(struct dev_pagemap *pgmap);
void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap);
@@ -215,6 +215,14 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn);
bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn);
unsigned long memremap_compat_align(void);
+
+static inline void zone_device_page_init(struct page *page)
+{
+ struct folio *folio = page_folio(page);
+
+ zone_device_folio_init(folio, 0);
I assume it is for legacy code, where only non-compound page exists?
It seems that you assume @page is always order-0, but there is no check
for it. Adding VM_WARN_ON_ONCE_FOLIO(folio_order(folio) != 0, folio)
above it would be useful to detect misuse.
+}
+
#else
static inline void *devm_memremap_pages(struct device *dev,
struct dev_pagemap *pgmap)
diff --git a/mm/memremap.c b/mm/memremap.c
index 46cb1b0b6f72..a8481ebf94cc 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -416,20 +416,19 @@ EXPORT_SYMBOL_GPL(get_dev_pagemap);
void free_zone_device_folio(struct folio *folio)
{
struct dev_pagemap *pgmap = folio->pgmap;
+ unsigned long nr = folio_nr_pages(folio);
+ int i;
if (WARN_ON_ONCE(!pgmap))
return;
mem_cgroup_uncharge(folio);
- /*
- * Note: we don't expect anonymous compound pages yet. Once supported
- * and we could PTE-map them similar to THP, we'd have to clear
- * PG_anon_exclusive on all tail pages.
- */
if (folio_test_anon(folio)) {
- VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
- __ClearPageAnonExclusive(folio_page(folio, 0));
+ for (i = 0; i < nr; i++)
+ __ClearPageAnonExclusive(folio_page(folio, i));
+ } else {
+ VM_WARN_ON_ONCE(folio_test_large(folio));
}
/*
@@ -456,8 +455,8 @@ void free_zone_device_folio(struct folio *folio)
case MEMORY_DEVICE_COHERENT:
if (WARN_ON_ONCE(!pgmap->ops || !pgmap->ops->page_free))
break;
- pgmap->ops->page_free(folio_page(folio, 0));
- put_dev_pagemap(pgmap);
+ pgmap->ops->page_free(&folio->page);
+ percpu_ref_put_many(&folio->pgmap->ref, nr);
break;
case MEMORY_DEVICE_GENERIC:
@@ -480,14 +479,23 @@ void free_zone_device_folio(struct folio *folio)
}
}
-void zone_device_page_init(struct page *page)
+void zone_device_folio_init(struct folio *folio, unsigned int order)
{
+ struct page *page = folio_page(folio, 0);
It is strange to see a folio is converted back to page in
a function called zone_device_folio_init().
+
+ VM_WARN_ON_ONCE(order > MAX_ORDER_NR_PAGES);
+
/*
* Drivers shouldn't be allocating pages after calling
* memunmap_pages().
*/
- WARN_ON_ONCE(!percpu_ref_tryget_live(&page_pgmap(page)->ref));
- set_page_count(page, 1);
+ WARN_ON_ONCE(!percpu_ref_tryget_many(&page_pgmap(page)->ref, 1 <<
order));
+ folio_set_count(folio, 1);
lock_page(page);
+
+ if (order > 1) {
+ prep_compound_page(page, order);
+ folio_set_large_rmappable(folio);
+ }
OK, so basically, @folio is not a compound page yet when
zone_device_folio_init()
is called.
I feel that your zone_device_page_init() and zone_device_folio_init()
implementations are inverse. They should follow the same pattern
as __alloc_pages_noprof() and __folio_alloc_noprof(), where
zone_device_page_init() does the actual initialization and
zone_device_folio_init() just convert a page to folio.
Something like:
void zone_device_page_init(struct page *page, unsigned int order)
{
VM_WARN_ON_ONCE(order > MAX_ORDER_NR_PAGES);
/*
* Drivers shouldn't be allocating pages after calling
* memunmap_pages().
*/
WARN_ON_ONCE(!percpu_ref_tryget_many(&page_pgmap(page)->ref, 1 << order));
/*
* anonymous folio does not support order-1, high order file-backed
folio
* is not supported at all.
*/
VM_WARN_ON_ONCE(order == 1);
if (order > 1)
prep_compound_page(page, order);
/* page has to be compound head here */
set_page_count(page, 1);
lock_page(page);
}
void zone_device_folio_init(struct folio *folio, unsigned int order)
{
struct page *page = folio_page(folio, 0);
zone_device_page_init(page, order);
page_rmappable_folio(page);
}
Or
struct folio *zone_device_folio_init(struct page *page, unsigned int order)
{
zone_device_page_init(page, order);
return page_rmappable_folio(page);
}
I think the problem is that it will all be weird once we dynamically
allocate "struct folio".
I have not yet a clear understanding on how that would really work.
For example, should it be pgmap->ops->page_folio() ?
Who allocates the folio? Do we allocate all order-0 folios initially, to
then merge them when constructing large folios? How do we manage the
"struct folio" during such merging splitting?
With that in mind, I don't really know what the proper interface should
be today.
zone_device_folio_init(struct page *page, unsigned int order)
looks cleaner, agreed.
Then, it comes to free_zone_device_folio() above,
I feel that pgmap->ops->page_free() should take an additional order
parameter to free a compound page like free_frozen_pages().
IIRC free_frozen_pages() does not operate on compound pages. If we know
that we are operating on a compound page (or single page) then passing
in the page (or better the folio) should work.
--
Cheers
David / dhildenb
