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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vP06Q-0000000DM7x-0Atr; Fri, 28 Nov 2025 15:09:42 +0000 Date: Fri, 28 Nov 2025 15:09:41 +0000 From: Matthew Wilcox To: Jordan Niethe Cc: linux-mm@kvack.org, balbirs@nvidia.com, matthew.brost@intel.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, david@redhat.com, ziy@nvidia.com, apopple@nvidia.com, lorenzo.stoakes@oracle.com, lyude@redhat.com, dakr@kernel.org, airlied@gmail.com, simona@ffwll.ch, rcampbell@nvidia.com, mpenttil@redhat.com, jgg@nvidia.com Subject: Re: [RFC PATCH 0/6] Remove device private pages from physical address space Message-ID: References: <20251128044146.80050-1-jniethe@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251128044146.80050-1-jniethe@nvidia.com> X-Stat-Signature: knjrwjy46f9hoaugfmehfj5tft34xzad X-Rspam-User: X-Rspamd-Queue-Id: 85C8614001B X-Rspamd-Server: rspam09 X-HE-Tag: 1764342586-478003 X-HE-Meta: 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 sMtxD9qG +yYHEoei32cm/JMFf+2VKVzPJrlfVvuZLK1IbWId5MFDIrGbm4zlU/7UUaTYFvhOOXdAiDw6d3O9TpMUwF6+MwD1YEPXEMCndktHlJN77N2dxavrk2s6au7ztfaygfqIycoj3Bu8mYtQpn2K7ngAGenLlv6bxhGtirvoBwRIQpMJetywzvDUrnTFJ2Iv9v5vi+lyBwu0iBu0X62NOo+WEPyzm87RSNo4SX6y8pAVw+E1/zBVQZTEwrSXzCIcPYOrQEtRt 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: On Fri, Nov 28, 2025 at 03:41:40PM +1100, Jordan Niethe wrote: > A consequence of placing the device private pages outside of the > physical address space is that they no longer have a PFN. However, it is > still necessary to be able to look up a corresponding device private > page from a device private PTE entry, which means that we still require > some way to index into this device private address space. This leads to > the idea of a device private PFN. This is like a PFN but instead of Don't call it a "device private PFN". That's going to lead to confusion. Device private index? Device memory index? > By removing the device private pages from the physical address space, > this RFC also opens up the possibility to moving away from tracking > device private memory using struct pages in the future. This is > desirable as on systems with large amounts of memory these device > private struct pages use a signifiant amount of memory and take a > significant amount of time to initialize. I did tell Jerome he was making a huge mistake with his design, but he forced it in anyway.