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

Boris Brezillon
2025-12-08T11:29:51Z

On Fri, 5 Dec 2025 19:22:21 +0100
Loïc Molinari <loic.molinari@collabora.com> wrote:

> 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

Queued to drm-misc-next.

>
> 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
>