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Thu, 16 Oct 2025 13:17:08 +0200 (CEST) Message-ID: Date: Thu, 16 Oct 2025 13:17:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 03/13] drm/shmem-helper: Map huge pages in fault handlers To: Matthew Wilcox Cc: 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_Canal?= , Hugh Dickins , Baolin Wang , Andrew Morton , Al Viro , =?UTF-8?Q?Miko=C5=82aj_Wasiak?= , Christian Brauner , Nitin Gote , Andi Shyti , Jonathan Corbet , Christopher Healy , Bagas Sanjaya , 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 References: <20251015153018.43735-1-loic.molinari@collabora.com> <20251015153018.43735-4-loic.molinari@collabora.com> Content-Language: fr From: =?UTF-8?Q?Lo=C3=AFc_Molinari?= Organization: Collabora Ltd In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Stat-Signature: m5be4ompig4sqfgwgjuwsnmpmjj9gqhy X-Rspam-User: X-Rspamd-Queue-Id: EB6F24000A X-HE-Tag: 1760613431-784847 X-HE-Meta: U2FsdGVkX19r2r3IUcFGtF4Ly+1ZTJX5IML/x0iQlapQkX/8MtVaiXsdpF560ro+SHj0iQo1eL4/cCYsUVZNWU3KUtJY3XZix5sdwmOIdEARY3GXlE9jh1Isz+hKboyNGCoBc5hdO5yyL4A2v6I0rsrVyisHwd+IFyenJNe/CrEL/2/TGDfORceHxZ8YUGA9EGnTOBJJAVfWQDXAQakVpCryPAkx/0MsblPMlDovQp2EsFsBjgKaoKfSVHDC0bEu5WsrpakE/lDEl9x9qQ2hZoRZ+v2GcvJgSJUYCCSbz2ocJ9aPfXq2pwvCTprpe2Xc1smfznTv39MgHs8LdLpCypCsaIrHCcpD84Pl198E6pW/awVH+KD7EUQ3rRAMoDT0SVTQ72HwIy8kDikqJmF8IpggzHs+Bl1ETBgpPphC/X2l/1gCgm/CvchjzGoxsS4SHBgzVOVJml8jo5hanLdt5DCwYTAT1J3Pf1zNdaS/mzpiUJ1/1EwB0nI8qIg4eWvt6x10dtftR/Em3Weg8lZ8qJWYm4yZGpMAHlpJoTxd70TTobbTMMUqOkIhpq4/Kx9K+TgN8kizXSSdi9szKdHkqpJdOvqeiQ8deGMRurYUH7jS45guygZ4pUAipxhOjHFxpbE5tAceWx6Hoz//dxBsrxW+/quO5BDCjuVM/WUZotVrN1hrJEg3jjNPozoJ9RGHtICASFHTcBSroIG1A5IDC9tWFupqdALChINCQXaHleomb8Ioiii3BH02PN46gloVOVc7GJ5RMU9KJU42ZOsFxSfy9M3GO3Xxp5hTwH+yuLdc7PzGju6xDIZpR2OxsY8kfagTcBDLInBFF1Ti7aHE2polg4wnmWeYYeF8YaM7OG+Uiojv3qCr+G6lAfSLlJwtaEyDFbtcAoqflr4fHmnVM8HSphORXhTbkjkfroatwjk+/GmZXPbdbGQC9dLWHZd96HI/1XJEfFAVfdAhYLM HBM43lW9 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Matthew, On 15/10/2025 19:27, Matthew Wilcox wrote: > On Wed, Oct 15, 2025 at 05:30:07PM +0200, Loïc Molinari wrote: > > This looks fine, no need to resend to fix this, but if you'd written > the previous patch slightly differently, you'd've reduced the amount of > code you moved around in this patch, which would have made it easier to > review. > >> + /* Map a range of pages around the faulty address. */ >> + do { >> + pfn = page_to_pfn(pages[start_pgoff]); >> + ret = vmf_insert_pfn(vma, addr, pfn); >> + addr += PAGE_SIZE; >> + } while (++start_pgoff <= end_pgoff && ret == VM_FAULT_NOPAGE); > > It looks to me like we have an opportunity to do better here by > adding a vmf_insert_pfns() interface. I don't think we should delay > your patch series to add it, but let's not forget to do that; it can > have very good performnce effects on ARM to use contptes. Agreed. I initially wanted to provide such an interface based on set_ptes() to benefit from arm64 contptes but thought it'd better be a distinct patch series. > >> @@ -617,8 +645,9 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf) > [...] >> >> - ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page)); >> + if (drm_gem_shmem_map_pmd(vmf, vmf->address, pages[page_offset])) { >> + ret = VM_FAULT_NOPAGE; >> + goto out; >> } > > Does this actually work? Yes, it does. Huge pages are successfully mapped from both map_pages and fault handlers. Anything wrong with it? There seems to be an another issue thought. There are failures [1], all looking like that one [2]. I think it's because map_pages is called with the RCU read lock taken and the DRM GEM map_pages handler must lock the GEM object before accessing pages with dma_resv_lock(). The locking doc says: "If it's not possible to reach a page without blocking, filesystem should skip it.". Unlocking the RCU read lock in the handler seems wrong and doing without a map_pages implementation would be unfortunate. What would you recommend here? Loïc [1] https://patchwork.freedesktop.org/series/156001/ [2] https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_156001v1/bat-dg1-7/igt@vgem_basic@dmabuf-mmap.html