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

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Message-ID: <20251208122941.61bea21d@fedora>
Date: Mon, 8 Dec 2025 12:29:41 +0100
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Loïc Molinari <loic.molinari@...labora.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
 <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Jani Nikula
 <jani.nikula@...ux.intel.com>, Joonas Lahtinen
 <joonas.lahtinen@...ux.intel.com>, Rodrigo Vivi <rodrigo.vivi@...el.com>,
 Tvrtko Ursulin <tursulin@...ulin.net>, Rob Herring <robh@...nel.org>,
 Steven Price <steven.price@....com>, Liviu Dudau <liviu.dudau@....com>,
 Melissa Wen <mwen@...lia.com>, Maíra Canal
 <mcanal@...lia.com>, Hugh Dickins <hughd@...gle.com>, Baolin Wang
 <baolin.wang@...ux.alibaba.com>, Andrew Morton <akpm@...ux-foundation.org>,
 Al Viro <viro@...iv.linux.org.uk>, Mikołaj Wasiak
 <mikolaj.wasiak@...el.com>, Christian Brauner <brauner@...nel.org>, Nitin
 Gote <nitin.r.gote@...el.com>, Andi Shyti <andi.shyti@...ux.intel.com>,
 Jonathan Corbet <corbet@....net>, Christopher Healy <healych@...zon.com>,
 Matthew Wilcox <willy@...radead.org>, Bagas Sanjaya <bagasdotme@...il.com>,
 linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 intel-gfx@...ts.freedesktop.org, linux-mm@...ck.org,
 linux-doc@...r.kernel.org, kernel@...labora.com
Subject: Re: [PATCH v13 00/10] drm: Reduce page tables overhead with THP

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