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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 BFFB917E1407; Tue, 21 Oct 2025 13:30:57 +0200 (CEST) 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 v5 03/12] drm/shmem-helper: Map huge pages in fault handlers Date: Tue, 21 Oct 2025 13:30:40 +0200 Message-ID: <20251021113049.17242-4-loic.molinari@collabora.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20251021113049.17242-1-loic.molinari@collabora.com> References: <20251021113049.17242-1-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 Check whether the starting address in the fault-around handler or the faulty address in the fault handler is part of a huge page in order to attempt a PMD sized PFN insertion into the VMA. On builds with CONFIG_TRANSPARENT_HUGEPAGE enabled, if the mmap() user address is PMD size aligned, if the GEM object is backed by shmem buffers on mountpoints setting the 'huge=3D' option and if the shmem backing store manages to allocate a huge folio, CPU mapping would then benefit from significantly increased memcpy() performance. When these conditions are met on a system with 2 MiB huge pages, an aligned copy of 2 MiB would raise a single page fault instead of 4096. v4: - implement map_pages instead of huge_fault Signed-off-by: Lo=C3=AFc Molinari --- drivers/gpu/drm/drm_gem_shmem_helper.c | 30 ++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_g= em_shmem_helper.c index 2a9fbc9c3712..b7238448d4f9 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -580,6 +580,26 @@ static bool drm_gem_shmem_fault_is_valid(struct drm_ge= m_object *obj, return true; } =20 +static bool drm_gem_shmem_map_pmd(struct vm_fault *vmf, unsigned long addr, + struct page *page) +{ +#ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP + unsigned long pfn =3D page_to_pfn(page); + unsigned long paddr =3D pfn << PAGE_SHIFT; + bool aligned =3D (addr & ~PMD_MASK) =3D=3D (paddr & ~PMD_MASK); + + if (aligned && + pmd_none(*vmf->pmd) && + folio_test_pmd_mappable(page_folio(page))) { + pfn &=3D PMD_MASK >> PAGE_SHIFT; + if (vmf_insert_pfn_pmd(vmf, pfn, false) =3D=3D VM_FAULT_NOPAGE) + return true; + } +#endif + + return false; +} + static vm_fault_t drm_gem_shmem_map_pages(struct vm_fault *vmf, pgoff_t start_pgoff, pgoff_t end_pgoff) @@ -606,6 +626,11 @@ static vm_fault_t drm_gem_shmem_map_pages(struct vm_fa= ult *vmf, goto out; } =20 + if (drm_gem_shmem_map_pmd(vmf, addr, pages[start_pgoff])) { + ret =3D VM_FAULT_NOPAGE; + goto out; + } + /* Map a range of pages around the faulty address. */ do { pfn =3D page_to_pfn(pages[start_pgoff]); @@ -639,6 +664,11 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault = *vmf) goto out; } =20 + if (drm_gem_shmem_map_pmd(vmf, vmf->address, pages[page_offset])) { + ret =3D VM_FAULT_NOPAGE; + goto out; + } + pfn =3D page_to_pfn(pages[page_offset]); ret =3D vmf_insert_pfn(vma, vmf->address, pfn); =20 --=20 2.47.3