[PATCH v13 00/10] drm: Reduce page tables overhead with THP

Loïc Molinari
2025-12-05T18:22:40Z

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 checking whether a faulty address in the page fault
handler 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.

Implementing a fault-around handler using the arm64 contiguous page
hint (contptes) could also greatly help reduce page tables overhead
for small pages by mapping several contiguous pages around a faulty
address at once. This will be proposed in another patch series.

Loïc Molinari (10):
drm/shmem-helper: Simplify page offset calculation in fault handler
drm/shmem-helper: Map huge pages in fault handler
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/panfrost: Introduce huge tmpfs mountpoint option
Documentation/gpu/drm-mm: Add THP paragraph to GEM mapping section

Documentation/gpu/drm-mm.rst | 29 ++-
drivers/gpu/drm/drm_gem.c | 202 +++++++++++++-----
drivers/gpu/drm/drm_gem_shmem_helper.c | 77 +++----
drivers/gpu/drm/i915/Makefile | 3 +-
.../gpu/drm/i915/gem/i915_gem_object_types.h | 9 +-
drivers/gpu/drm/i915/gem/i915_gem_shmem.c | 58 +++--
drivers/gpu/drm/i915/gem/i915_gemfs.c | 71 ------
drivers/gpu/drm/i915/gem/i915_gemfs.h | 14 --
.../gpu/drm/i915/gem/selftests/huge_pages.c | 15 +-
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/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 | 21 +-
drivers/gpu/drm/v3d/v3d_gemfs.c | 62 ------
include/drm/drm_device.h | 15 ++
include/drm/drm_gem.h | 40 +++-
include/drm/drm_gem_shmem_helper.h | 3 -
29 files changed, 420 insertions(+), 303 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