From nobody Mon Dec 1 22:36:48 2025 Received: from bali.collaboradmins.com (bali.collaboradmins.com [148.251.105.195]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 54A5333508A; Fri, 28 Nov 2025 18:53:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.251.105.195 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764355989; cv=none; b=FnGlaOHBrXoq3wTcGwVa3KIQCSdTiJ7HZ5chmTt9nOohG/x5mx87NSnPvx+3LA+hF2jm8GohRyXWmx6pCO8SpZSPKkeFj+LojD2J8RFcSiyEBf6p9VWjt5iMRspkHeNbvcIuI5q0v0OsHyCky0M7MiYwyro4sRKHWoDr8iR0Eos= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764355989; c=relaxed/simple; bh=40WG8/2e61IMWsDRpUFUHulUyBgQPDILQimEoI6b3o0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=a2pkiSaccTyez2TkoLw6N8VwRU5xjKP4RUlXUCfetPnaTSruQl9ly+DpAKkdgrmgGPCo9n401ZQgaGUuao9w2TJWRJtlpICQQ3UfzOti4a1dbt1CoxxqxvfaIZjIb08oiqCAG7V+oe7k0q/dnr4MFxGnsRCpnNPoPQI4gtaFO7g= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b=iiuP44ez; arc=none smtp.client-ip=148.251.105.195 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b="iiuP44ez" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1764355985; bh=40WG8/2e61IMWsDRpUFUHulUyBgQPDILQimEoI6b3o0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iiuP44ezth3Y2JRlmZ1rSE+K74/8kwjO/TPviOWbw1FSgy5A9odQ4CmhNAS5FVvQq UDUaAtfuZSRBLv9FRfg1M15w3uCVYBCbZp0VhNqgFw1Smij4a4R0cxQ2SZPoqyVLjs AicmW2MlD5NO/bI58Q1fdMnkdKQD81oGc+uqKsSy2v6JMGfPxWJu30MP+o9FCc+8bj MqE4JUcRg56N4kiMmPZFPZ1kcn4TdiLtIetYmohoFTLM7HszF2ESw4xMNCkK066M3E ekn+f5BdBYQCBcxHmdv8/kuL5yYEWyY8TAOYBqrsD84n1ISi9RjJnAxjxKgCzWmRZt rwpbMBoLk7bYw== Received: from debian-rockchip-rock5b-rk3588.. (unknown [IPv6:2a01:e0a:5e3:6100:2e0:4cff:fe03:d8c]) (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 10AC217E1423; Fri, 28 Nov 2025 19:53:05 +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 v10 10/10] Documentation/gpu/drm-mm: Add THP paragraph to GEM mapping section Date: Fri, 28 Nov 2025 19:52:52 +0100 Message-ID: <20251128185252.3092-11-loic.molinari@collabora.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20251128185252.3092-1-loic.molinari@collabora.com> References: <20251128185252.3092-1-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 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 Signed-off-by: Lo=C3=AFc Molinari Reviewed-by: Bagas Sanjaya Reviewed-by: Boris Brezillon --- Documentation/gpu/drm-mm.rst | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-) diff --git a/Documentation/gpu/drm-mm.rst b/Documentation/gpu/drm-mm.rst index d55751cad67c..d69eab0b4093 100644 --- a/Documentation/gpu/drm-mm.rst +++ b/Documentation/gpu/drm-mm.rst @@ -290,15 +290,27 @@ 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