[PATCH v4 0/6] drm/gem-shmem: Track page accessed/dirty status

Thomas Zimmermann
2026-02-27T11:45:22Z

Track page access/dirty status in gem-shmem for better integration with
the overall memory management. Gem-shmem has long had two flag bits in
struct drm_gem_shmem_object, named pages_mark_accessed_on_put and
pages_mark_dirty_on_put, but never used them much; except for some odd
cases in drivers. Therefore pages in gem-shmem where never marked
correctly. (Other DRM memory managers do some course-grain tracking at
least).

Patches 1 to 4 prepare the mmap page-fault handler for tracking page
status easily. The pages are already available; only the mmap handling
needs to be adapted. The way the shmem code interacts with huge-page
support is also not optimal, hence refactor it slightly.

Patch 5 adds tracking access and dirty status in mmap. With the earlier
patches, this change simply falls into place.

Patch 6 adds tracking access and dirty status in vmap. Because there's
no fault handling here, we refer to the existing status bits in struct
drm_gem_shmem_object. Each page's status will be updated by the page
release in drm_gem_put_pages(). The imagination driver requires a small
fix to make it work correctly.

Tested with CONFIG_VM=y by running animations on DRM's bochs driver for
several hours. This uses gem-shmem's mmap and vmap extensively.

v4:
- mark folio as accessed on VM_FAULT_NOPAGE (Boris)
- validate state in mkwrite (Boris)
v3:
- rewrite for VM_PFNMAP
- do more preparational patches
v2:
- fix possible OOB access into page array (Matthew)
- simplify fault-handler error handling (Boris)
- simplify internal interfaces (Matthew)

Thomas Zimmermann (6):
drm/gem-shmem: Use obj directly where appropriate in fault handler
drm/gem-shmem: Test for existence of page in mmap fault handler
drm/gem-shmem: Return vm_fault_t from drm_gem_shmem_try_map_pmd()
drm/gem-shmem: Refactor drm_gem_shmem_try_map_pmd()
drm/gem-shmem: Track folio accessed/dirty status in mmap
drm/gem-shmem: Track folio accessed/dirty status in vmap

drivers/gpu/drm/drm_gem_shmem_helper.c | 79 +++++++++++++++++---------
drivers/gpu/drm/imagination/pvr_gem.c | 6 +-
2 files changed, 55 insertions(+), 30 deletions(-)

base-commit: 1c44015babd759b8e5234084dffcc08a0b784333
--
2.52.0