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Thu, 30 Jan 2025 05:06:15 -0800 (PST) Received: from phenom.ffwll.local ([2a02:168:57f4:0:5485:d4b2:c087:b497]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38c5c125f77sm1959273f8f.56.2025.01.30.05.06.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Jan 2025 05:06:15 -0800 (PST) Date: Thu, 30 Jan 2025 14:06:12 +0100 From: Simona Vetter To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, nouveau@lists.freedesktop.org, Andrew Morton , =?iso-8859-1?B?Suly9G1l?= Glisse , Jonathan Corbet , Alex Shi , Yanteng Si , Karol Herbst , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pasha Tatashin , Peter Xu , Alistair Popple , Jason Gunthorpe Subject: Re: [PATCH v1 08/12] mm/rmap: handle device-exclusive entries correctly in try_to_unmap_one() Message-ID: Mail-Followup-To: David Hildenbrand , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, nouveau@lists.freedesktop.org, Andrew Morton , =?iso-8859-1?B?Suly9G1l?= Glisse , Jonathan Corbet , Alex Shi , Yanteng Si , Karol Herbst , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pasha Tatashin , Peter Xu , Alistair Popple , Jason Gunthorpe References: <20250129115411.2077152-1-david@redhat.com> <20250129115411.2077152-9-david@redhat.com> <59feb709-dadc-4d19-857e-49320cca3d98@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <59feb709-dadc-4d19-857e-49320cca3d98@redhat.com> X-Operating-System: Linux phenom 6.12.11-amd64 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 348B8120010 X-Stat-Signature: ka3wxggjgqzx6ddnbs4earogsdmm7r8w X-Rspam-User: X-HE-Tag: 1738242377-27645 X-HE-Meta: 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 Cd84Swdi FgsOq2/+MBmm7GGFGfIvohUvb2WYhiPX0s6KLNWTYhgaPaDujeq0Ud0i+uDXKDoFC4uVx4b6YLwRn26Q2lMtygbiQAxmEXhbT5vbzl/SPJv1Rl8RKftjZAzw/wz6Sz9KKNqfyyVHbrtpmWqTYNhl42+qBGnNV18v9DK3JvxyfG0l8TxLJRgMSZhZAD1Yaj3rxD5CginkBVrnwYbFi7dMkJ+xrhLh8KL/tg9YkVB6UWsuFH87FrVji7i16VMUF7kBR4Am9TEq2N6oRvinDgMbmaG8k2NEuLs6uUwCbBdZCLWYs86U8A3ZZjI3Wd9fiyVRXruRK/EtXLAPy+mAtlKAIyZbXaw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.004970, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jan 30, 2025 at 12:08:42PM +0100, David Hildenbrand wrote: > On 30.01.25 11:10, Simona Vetter wrote: > > On Wed, Jan 29, 2025 at 12:54:06PM +0100, David Hildenbrand wrote: > > > Ever since commit b756a3b5e7ea ("mm: device exclusive memory access") > > > we can return with a device-exclusive entry from page_vma_mapped_walk(). > > > > > > try_to_unmap_one() is not prepared for that, so teach it about these > > > non-present nonswap PTEs. > > > > > > Before that, could we also have triggered this case with device-private > > > entries? Unlikely. > > > > Just quick comment on this, I'm still pondering all the other aspects. > > > > device-private memory is entirely owned by the driver, the core mm isn't > > supposed to touch these beyond migrating it back to system memory in > > do_swap_page. Plus using rmap when the driver asks for invalidating > > mappings as needed. > > > > So no lru, thp, migration or anything initiated by core mm should ever > > happen on these device private pages. If it does, it'd be a bug. > > I was not 100% sure about HWPoison handling, that's why I added that > comment. In other regards I agree: reclaim etc. does not apply. So maybe I'm just entirely lost, but unless you have a coherent interconnect I don't think hwpoisin should get involved with device private memory? And for a coherent interconnect it's just device memory, which isn't treated very special. Also to clarify, I meant this as a general comment for all subsequent patches that have the same paragraph. -Sima -- Simona Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch