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(unknown [IPv6:2a01:e0a:5e3:6100:826d:bc07:e98c:84a]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: loicmolinari) by bali.collaboradmins.com (Postfix) with ESMTPSA id 2198D17E12D5; Fri, 5 Dec 2025 19:22:44 +0100 (CET) From: =?UTF-8?q?Lo=C3=AFc=20Molinari?= To: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , Boris Brezillon , Rob Herring , Steven Price , Liviu Dudau , Melissa Wen , =?UTF-8?q?Ma=C3=ADra=20Canal?= , Hugh Dickins , Baolin Wang , Andrew Morton , =?UTF-8?q?Lo=C3=AFc=20Molinari?= , Al Viro , =?UTF-8?q?Miko=C5=82aj=20Wasiak?= , Christian Brauner , Nitin Gote , Andi Shyti , Jonathan Corbet , Christopher Healy , Matthew Wilcox , Bagas Sanjaya Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, kernel@collabora.com Subject: [PATCH v13 10/10] Documentation/gpu/drm-mm: Add THP paragraph to GEM mapping section Date: Fri, 5 Dec 2025 19:22:31 +0100 Message-ID: <20251205182231.194072-11-loic.molinari@collabora.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20251205182231.194072-1-loic.molinari@collabora.com> References: <20251205182231.194072-1-loic.molinari@collabora.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Add a paragraph to the GEM Objects Creation section about the drm_gem_huge_mnt_create() helper and to the GEM objects mapping section explaining how transparent huge pages are handled by GEM. v4: - fix wording after huge_pages handler removal v6: - fix wording after map_pages handler removal v11: - mention drm_gem_huge_mnt_create() helper - add Boris and Ma=C3=ADra R-bs Signed-off-by: Lo=C3=AFc Molinari Reviewed-by: Bagas Sanjaya Reviewed-by: Boris Brezillon Reviewed-by: Ma=C3=ADra Canal --- Documentation/gpu/drm-mm.rst | 29 +++++++++++++++++++++++------ 1 file changed, 23 insertions(+), 6 deletions(-) diff --git a/Documentation/gpu/drm-mm.rst b/Documentation/gpu/drm-mm.rst index d55751cad67c..f22433470c76 100644 --- a/Documentation/gpu/drm-mm.rst +++ b/Documentation/gpu/drm-mm.rst @@ -155,7 +155,12 @@ drm_gem_object_init() will create an shmfs file of the requested size and store it into the struct :c:type:`struct drm_gem_object ` filp field. The memory is used as either main storage for the object when the graphics hardware -uses system memory directly or as a backing store otherwise. +uses system memory directly or as a backing store otherwise. Drivers +can call drm_gem_huge_mnt_create() to create, mount and use a huge +shmem mountpoint instead of the default one ('shm_mnt'). For builds +with CONFIG_TRANSPARENT_HUGEPAGE enabled, further calls to +drm_gem_object_init() will let shmem allocate huge pages when +possible. =20 Drivers are responsible for the actual physical pages allocation by calling shmem_read_mapping_page_gfp() for each page. @@ -290,15 +295,27 @@ The open and close operations must update the GEM obj= ect reference count. Drivers can use the drm_gem_vm_open() and drm_gem_vm_close() helper functions directly as open and close handlers. =20 -The fault operation handler is responsible for mapping individual pages -to userspace when a page fault occurs. Depending on the memory -allocation scheme, drivers can allocate pages at fault time, or can -decide to allocate memory for the GEM object at the time the object is -created. +The fault operation handler is responsible for mapping pages to +userspace when a page fault occurs. Depending on the memory allocation +scheme, drivers can allocate pages at fault time, or can decide to +allocate memory for the GEM object at the time the object is created. =20 Drivers that want to map the GEM object upfront instead of handling page faults can implement their own mmap file operation handler. =20 +In order to reduce page table overhead, if the internal shmem mountpoint +"shm_mnt" is configured to use transparent huge pages (for builds with +CONFIG_TRANSPARENT_HUGEPAGE enabled) and if the shmem backing store +managed to allocate a huge page for a faulty address, the fault handler +will first attempt to insert that huge page into the VMA before falling +back to individual page insertion. mmap() user address alignment for GEM +objects is handled by providing a custom get_unmapped_area file +operation which forwards to the shmem backing store. For most drivers, +which don't create a huge mountpoint by default or through a module +parameter, transparent huge pages can be enabled by either setting the +"transparent_hugepage_shmem" kernel parameter or the +"/sys/kernel/mm/transparent_hugepage/shmem_enabled" sysfs knob. + For platforms without MMU the GEM core provides a helper method drm_gem_dma_get_unmapped_area(). The mmap() routines will call this to get= a proposed address for the mapping. --=20 2.47.3