On 9/18/25 12:49, 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 <balb...@nvidia.com>
>> Cc: David Hildenbrand <da...@redhat.com>
>> Cc: Zi Yan <z...@nvidia.com>
>> Cc: Joshua Hahn <joshua.hah...@gmail.com>
>> Cc: Rakie Kim <rakie....@sk.com>
>> Cc: Byungchul Park <byungc...@sk.com>
>> Cc: Gregory Price <gou...@gourry.net>
>> Cc: Ying Huang <ying.hu...@linux.alibaba.com>
>> Cc: Alistair Popple <apop...@nvidia.com>
>> Cc: Oscar Salvador <osalva...@suse.de>
>> Cc: Lorenzo Stoakes <lorenzo.stoa...@oracle.com>
>> Cc: Baolin Wang <baolin.w...@linux.alibaba.com>
>> Cc: "Liam R. Howlett" <liam.howl...@oracle.com>
>> Cc: Nico Pache <npa...@redhat.com>
>> Cc: Ryan Roberts <ryan.robe...@arm.com>
>> Cc: Dev Jain <dev.j...@arm.com>
>> Cc: Barry Song <bao...@kernel.org>
>> Cc: Lyude Paul <ly...@redhat.com>
>> Cc: Danilo Krummrich <d...@kernel.org>
>> Cc: David Airlie <airl...@gmail.com>
>> Cc: Simona Vetter <sim...@ffwll.ch>
>> Cc: Ralph Campbell <rcampb...@nvidia.com>
>> Cc: Mika Penttilä <mpent...@redhat.com>
>> Cc: Matthew Brost <matthew.br...@intel.com>
>> Cc: Francois Dugast <francois.dug...@intel.com>
>> ---
>> 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);
> }
>
>
> 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().
>
>
> This is my impression after reading the patch and zone device page code.
>
> Alistair and David can correct me if this is wrong, since I am new to
> zone device page code.
>
Thanks, I did not want to change zone_device_page_init() for several
drivers (outside my test scope) that already assume it has an order size of 0.
Balbir Singh
