[PATCH v5 00/12] drm: Reduce page tables overhead with THP

Loïc Molinari
2025-10-21T11:30:57Z

This series aims to reduce the page tables overhead of DRM drivers for
builds with CONFIG_TRANSPARENT_HUGEPAGE enabled and either the sysfs
knob '/sys/kernel/mm/transparent_hugepage/shmem_enabled' appropriately
set or drivers using a dedicated huge tmpfs mount point.

It starts by implementing a map_pages handler for GEM objects to map
pages around a faulty address in a single batch. It also checks in
both the fault and fault-around handlers whether a faulty address is
part of a huge page in order to attempt a PMD sized PFN insertion into
the VMA. It then introduces a dedicated get_unmapped_area file
operation on the DRM file descriptor for GEM objects to get the best
virtual address alignment for the underlying shmem buffers.

The remaining commits propose shmem helpers to create and release huge
tmpfs mount points and adapt the i915 and V3D drivers. The helpers are
then used to optionally enable Transparent Hugepage for Panfrost and
Panthor.

For Panthor on a Rock 5B, this series makes the first memcpy() to an
entire BO object mapped in userspace about twice as fast with
Transparent Hugepage enabled.

Note that some architectures like arm64 with the contiguous page hint
(contptes) would very likely benefit from a vmf_insert_pfns() function
based on set_ptes() to insert a range of contiguous ptes.

Loïc Molinari (12):
drm/shmem-helper: Simplify page offset calculation in fault handler
drm/shmem-helper: Implement map_pages fault-around handler
drm/shmem-helper: Map huge pages in fault handlers
drm/gem: Introduce drm_gem_get_unmapped_area() fop
drm/gem: Add huge tmpfs mountpoint helpers
drm/i915: Use huge tmpfs mountpoint helpers
drm/v3d: Use huge tmpfs mountpoint helpers
drm/gem: Get rid of *_with_mnt helpers
drm/panthor: Introduce huge tmpfs mountpoint option
drm/panthor: Improve IOMMU map/unmap debugging logs
drm/panfrost: Introduce huge tmpfs mountpoint option
Documentation/gpu/drm-mm: Add THP paragraph to GEM mapping section

Documentation/gpu/drm-mm.rst | 25 ++-
drivers/gpu/drm/drm_gem.c | 184 +++++++++++++-----
drivers/gpu/drm/drm_gem_shmem_helper.c | 142 ++++++++++----
drivers/gpu/drm/i915/Makefile | 3 +-
drivers/gpu/drm/i915/gem/i915_gem_shmem.c | 47 +++--
drivers/gpu/drm/i915/gem/i915_gemfs.c | 69 -------
drivers/gpu/drm/i915/gem/i915_gemfs.h | 14 --
.../gpu/drm/i915/gem/selftests/huge_pages.c | 11 +-
drivers/gpu/drm/i915/i915_drv.h | 5 -
drivers/gpu/drm/panfrost/panfrost_device.c | 3 +
drivers/gpu/drm/panfrost/panfrost_drv.c | 6 +
drivers/gpu/drm/panfrost/panfrost_drv.h | 9 +
drivers/gpu/drm/panfrost/panfrost_gem.c | 18 ++
drivers/gpu/drm/panfrost/panfrost_gem.h | 2 +
drivers/gpu/drm/panthor/panthor_device.c | 3 +
drivers/gpu/drm/panthor/panthor_drv.c | 7 +
drivers/gpu/drm/panthor/panthor_drv.h | 9 +
drivers/gpu/drm/panthor/panthor_gem.c | 18 ++
drivers/gpu/drm/panthor/panthor_gem.h | 2 +
drivers/gpu/drm/panthor/panthor_mmu.c | 19 +-
drivers/gpu/drm/v3d/Makefile | 3 +-
drivers/gpu/drm/v3d/v3d_bo.c | 6 +-
drivers/gpu/drm/v3d/v3d_drv.c | 2 +-
drivers/gpu/drm/v3d/v3d_drv.h | 11 +-
drivers/gpu/drm/v3d/v3d_gem.c | 27 ++-
drivers/gpu/drm/v3d/v3d_gemfs.c | 60 ------
include/drm/drm_device.h | 15 ++
include/drm/drm_gem.h | 59 +++++-
include/drm/drm_gem_shmem_helper.h | 3 -
mm/shmem.c | 1 +
30 files changed, 491 insertions(+), 292 deletions(-)
delete mode 100644 drivers/gpu/drm/i915/gem/i915_gemfs.c
delete mode 100644 drivers/gpu/drm/i915/gem/i915_gemfs.h
create mode 100644 drivers/gpu/drm/panfrost/panfrost_drv.h
create mode 100644 drivers/gpu/drm/panthor/panthor_drv.h
delete mode 100644 drivers/gpu/drm/v3d/v3d_gemfs.c

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2.47.3