Re: [v7 01/16] mm/zone_device: support large zone device private folios

[Balbir Singh <balbirs@nvidia.com>]

On 10/12/25 17:10, Lance Yang wrote:
> Hi Balbir,
> 
> Just one nit below :)
> 
> On Wed, Oct 1, 2025 at 3:43 PM Balbir Singh <balbirs@nvidia.com> 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 <balbirs@nvidia.com>
>> 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>
>> Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
>> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
>> Cc: Felix Kuehling <Felix.Kuehling@amd.com>
>> Cc: Alex Deucher <alexander.deucher@amd.com>
>> Cc: "Christian König" <christian.koenig@amd.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> ---
>>  arch/powerpc/kvm/book3s_hv_uvmem.c       |  2 +-
>>  drivers/gpu/drm/amd/amdkfd/kfd_migrate.c |  2 +-
>>  drivers/gpu/drm/drm_pagemap.c            |  2 +-
>>  drivers/gpu/drm/nouveau/nouveau_dmem.c   |  2 +-
>>  include/linux/memremap.h                 | 10 ++++++++-
>>  lib/test_hmm.c                           |  2 +-
>>  mm/memremap.c                            | 26 ++++++++++++++----------
>>  mm/rmap.c                                |  6 +++++-
>>  8 files changed, 34 insertions(+), 18 deletions(-)
>>
>> diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
>> index 03f8c34fa0a2..91f763410673 100644
>> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
>> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
>> @@ -723,7 +723,7 @@ static struct page *kvmppc_uvmem_get_page(unsigned long gpa, struct kvm *kvm)
>>
>>         dpage = pfn_to_page(uvmem_pfn);
>>         dpage->zone_device_data = pvt;
>> -       zone_device_page_init(dpage);
>> +       zone_device_page_init(dpage, 0);
>>         return dpage;
>>  out_clear:
>>         spin_lock(&kvmppc_uvmem_bitmap_lock);
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
>> index 79251f22b702..d0e2cae33035 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
>> @@ -217,7 +217,7 @@ svm_migrate_get_vram_page(struct svm_range *prange, unsigned long pfn)
>>         page = pfn_to_page(pfn);
>>         svm_range_bo_ref(prange->svm_bo);
>>         page->zone_device_data = prange->svm_bo;
>> -       zone_device_page_init(page);
>> +       zone_device_page_init(page, 0);
>>  }
>>
>>  static void
>> diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
>> index 1da55322af12..31c53f724e25 100644
>> --- a/drivers/gpu/drm/drm_pagemap.c
>> +++ b/drivers/gpu/drm/drm_pagemap.c
>> @@ -196,7 +196,7 @@ static void drm_pagemap_get_devmem_page(struct page *page,
>>                                         struct drm_pagemap_zdd *zdd)
>>  {
>>         page->zone_device_data = drm_pagemap_zdd_get(zdd);
>> -       zone_device_page_init(page);
>> +       zone_device_page_init(page, 0);
>>  }
>>
>>  /**
>> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
>> index ca4932a150e3..53cc1926b9da 100644
>> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
>> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
>> @@ -318,7 +318,7 @@ nouveau_dmem_page_alloc_locked(struct nouveau_drm *drm)
>>                         return NULL;
>>         }
>>
>> -       zone_device_page_init(page);
>> +       zone_device_page_init(page, 0);
>>         return page;
>>  }
>>
>> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
>> index e5951ba12a28..d2487a19cba2 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_page_init(struct page *page, 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_folio_init(struct folio *folio, unsigned int order)
>> +{
>> +       zone_device_page_init(&folio->page, order);
>> +       if (order)
>> +               folio_set_large_rmappable(folio);
>> +}
>> +
>>  #else
>>  static inline void *devm_memremap_pages(struct device *dev,
>>                 struct dev_pagemap *pgmap)
>> diff --git a/lib/test_hmm.c b/lib/test_hmm.c
>> index 83e3d8208a54..24d82121cde8 100644
>> --- a/lib/test_hmm.c
>> +++ b/lib/test_hmm.c
>> @@ -627,7 +627,7 @@ static struct page *dmirror_devmem_alloc_page(struct dmirror_device *mdevice)
>>                         goto error;
>>         }
>>
>> -       zone_device_page_init(dpage);
>> +       zone_device_page_init(dpage, 0);
>>         dpage->zone_device_data = rpage;
>>         return dpage;
>>
>> diff --git a/mm/memremap.c b/mm/memremap.c
>> index 46cb1b0b6f72..e45dfb568710 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);
> 
> Nit: &pgmap->ref here for consistency?

Can be done, thanks!

Balbir