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b=m9Ur08k8fMZRkAAhCI2CxUvgZeupcT7GIrwX+p9fSpvfV3Ajb3FbMQVykY2lKtAQe rcSRUeEGnf3/NMWyPQ0qugpcciD3AvqI+F+GniZhsF5a2Ryvk/XXb2nshNIIN+x5cR JYlU5fpj2U7s/S3WdPrOsq+Y0apgFmjxkWh8sXtE1wxekMHk5W9Gzb05gDZS+Vgjfn oho/ytmj/aLCNS2l7wFW8/VHiNHcb8DPqS3CMWOxTVqp1CjPVVhuNpZCOYebRtk4tZ ZLlxV+n2Jb/jAlskHje+GtPWM7FPyNyourFaqabkHce71qm183YbuQjYPsdqdZX51N JlOQHRHBYPBPw== Date: Mon, 24 Mar 2025 14:18:34 -0400 From: Mike Rapoport To: Jason Gunthorpe Cc: Changyuan Lyu , linux-kernel@vger.kernel.org, graf@amazon.com, akpm@linux-foundation.org, luto@kernel.org, anthony.yznaga@oracle.com, arnd@arndb.de, ashish.kalra@amd.com, benh@kernel.crashing.org, bp@alien8.de, catalin.marinas@arm.com, dave.hansen@linux.intel.com, dwmw2@infradead.org, ebiederm@xmission.com, mingo@redhat.com, jgowans@amazon.com, corbet@lwn.net, krzk@kernel.org, mark.rutland@arm.com, pbonzini@redhat.com, pasha.tatashin@soleen.com, hpa@zytor.com, peterz@infradead.org, ptyadav@amazon.de, robh+dt@kernel.org, robh@kernel.org, saravanak@google.com, skinsburskii@linux.microsoft.com, rostedt@goodmis.org, tglx@linutronix.de, thomas.lendacky@amd.com, usama.arif@bytedance.com, will@kernel.org, devicetree@vger.kernel.org, kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org Subject: Re: [PATCH v5 09/16] kexec: enable KHO support for memory preservation Message-ID: References: <20250320015551.2157511-1-changyuanl@google.com> <20250320015551.2157511-10-changyuanl@google.com> <20250321134629.GA252045@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: E2E55C0017 X-Rspamd-Server: rspam05 X-Rspam-User: X-Stat-Signature: 9a9q8joyga145a37cd78bwbz9uxoep8b X-HE-Tag: 1742840320-560678 X-HE-Meta: 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 oYYh+6+W vz67xoXuSalWwVyAXU6tAcEpgM9sWcKoApzwgB0akQaKbTJCf7YSlEh/iamQIeQrIclwKFjuDtjtZKun9MG36Zt3cbDu2QJkF8KhSi5/b/hUyXANqMr/pZMJfpi4T3DLvkA0slqU6DtWjIGwcvZlYzgueOYp0SmhE7KjVV9lPcGzwJ1riXR0slRs+1ywIUp4K+BKf5xKoDkVKu0KoWKpoipxjWQul9stBb1+RWFw+/v1LujthH/plJ3GbzB/h2AKXtE4Mmm48jg87ji4iBUfvH88yofPQIvYmdOPPKbipOeqMwVzOgQXMX6ocLpxNwh4Wbn1d/d2Ju0mhGnelKHtYGa7+uN+pds9J2riCX6esPpbUgcFRSjfasI+tUNVvgNwdnN+IJOTkiAWcqPuccyv6qQwqM0mHZ4DlDuVu 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 Sun, Mar 23, 2025 at 03:55:52PM -0300, Jason Gunthorpe wrote: > On Sat, Mar 22, 2025 at 03:12:26PM -0400, Mike Rapoport wrote: > > > > > + page->private = order; > > > > > > Can't just set the page order directly? Why use private? > > > > Setting the order means recreating the folio the way prep_compound_page() > > does. I think it's better to postpone it until the folio is requested. This > > way it might run after SMP is enabled. > > I see, that makes sense, but also it could stil use page->order.. But there's no page->order :) > > Besides, when we start allocating > > folios separately from struct page, initializing it here would be a real > > issue. > > Yes, but also we wouldn't have page->private to make it work.. Somehow > anything we want to carry over would have to become encoded in the > memdesc directly. This is a problem to solve in 2026 :) The January update for State of Page [1] talks about reasonable goal to shrink struct page to (approximately): struct page { unsigned long flags; union { struct list_head buddy_list; struct list_head pcp_list; struct { unsigned long memdesc; int _refcount; }; }; union { unsigned long private; struct { int _folio_mapcount; }; }; }; [1] https://lore.kernel.org/linux-mm/Z37pxbkHPbLYnDKn@casper.infradead.org/ > Jason -- Sincerely yours, Mike.