[RFC PATCH v1 00/10] mm: Introduce and use folio_owner_ops

[Fuad Tabba <tabba@google.com>]

Some folios, such as hugetlb folios and zone device folios,
require special handling when the folio's reference count reaches
0, before being freed. Moreover, guest_memfd folios will likely
require special handling to notify it once a folio's reference
count reaches 0, to facilitate shared to private folio conversion
[*]. Currently, each usecase has a dedicated callback when the
folio refcount reaches 0 to that effect. Adding yet more
callbacks is not ideal.

This patch series introduces struct folio_owner_ops and uses it
as a generic way to handle callbacks on freeing a folio. It also
applies the callbacks to hugetlb and zone device folios.

A pointer to struct folio_owner_ops is overlaid on struct page
compound_page, struct page/folio lru. To indicate that the folio
uses the callback, this patch series sets bit 1 of the new field,
similar to how bit 0 indicates a compound page.

Patches 1 to 6 rework the hugetlb code to allow us to reuse
folio->lru for the owner ops as long as they are not isolated.

Patches 7 to 10 introduce struct folio_owner_ops, and apply the
callbacks to zone device and hugetlb folios.

Cheers,
/fuad

[*] https://lore.kernel.org/all/CAGtprH_JP2w-4rq02h_Ugvq5KuHX7TUvegOS7xUs_iy5hriE7g@mail.gmail.com/

David Hildenbrand (6):
  mm/hugetlb: rename isolate_hugetlb() to folio_isolate_hugetlb()
  mm/migrate: don't call folio_putback_active_hugetlb() on dst hugetlb
    folio
  mm/hugetlb: rename "folio_putback_active_hugetlb()" to
    "folio_putback_hugetlb()"
  mm/hugetlb-cgroup: convert hugetlb_cgroup_css_offline() to work on
    folios
  mm/hugetlb: use folio->lru int demote_free_hugetlb_folios()
  mm/hugetlb: use separate folio->_hugetlb_list for hugetlb-internals

Fuad Tabba (4):
  mm: Introduce struct folio_owner_ops
  mm: Use getters and setters to access page pgmap
  mm: Use owner_ops on folio_put for zone device pages
  mm: hugetlb: Use owner_ops on folio_put for hugetlb

 drivers/gpu/drm/nouveau/nouveau_dmem.c |   4 +-
 drivers/pci/p2pdma.c                   |   8 +-
 include/linux/hugetlb.h                |  10 +-
 include/linux/memremap.h               |  14 +-
 include/linux/mm_types.h               | 107 ++++++++++++++-
 lib/test_hmm.c                         |   2 +-
 mm/gup.c                               |   2 +-
 mm/hmm.c                               |   2 +-
 mm/hugetlb.c                           | 179 ++++++++++++++++++-------
 mm/hugetlb_cgroup.c                    |  19 ++-
 mm/hugetlb_vmemmap.c                   |   8 +-
 mm/internal.h                          |   1 -
 mm/memory.c                            |   2 +-
 mm/mempolicy.c                         |   2 +-
 mm/memremap.c                          |  49 +------
 mm/migrate.c                           |  20 +--
 mm/migrate_device.c                    |   4 +-
 mm/mm_init.c                           |  48 ++++++-
 mm/swap.c                              |  25 ++--
 19 files changed, 342 insertions(+), 164 deletions(-)


base-commit: beb2622b970047000fa3cae64c23585669b01fca
-- 
2.47.0.277.g8800431eea-goog