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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1743005913; bh=62UK7sgqLy7YlWGLIBWH0rQyGMv0oNWe5Wt7OkG2t2o=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=LdR103iIgMle3veCG5V4CzGebSd89g32/pXSAVfRo0VtzYkq549g6URwrOkAOoMTp ZNz9gVD6klRNX6tPCqdnyua9NDkzPvB5i5TX7icqz62+gERX61O5MwWASeAokKPmSg IBoKfCRXBjo6J3bIdmWdI/ng4e05Y04Pa/auc91ohtFbQR8WjixNnuH21lmrX05eig 8ZlDmEoIvsFD1gf0ksYdPaBa3g8DdAQ3J8swuXuls1/BaC6DPxcB7iecUNO0ZHwccO pJNCcu832sqa5MuG7poxR/cUHswABVzUPNiRRoCcbyesdTSbL/69UEjph0YWiw58OX YAF2ZRD++0lrQ== From: Pratyush Yadav To: Jason Gunthorpe Cc: Pratyush Yadav , David Rientjes , Alexander Graf , Anthony Yznaga , Dave Hansen , David Hildenbrand , Frank van der Linden , James Gowans , Junaid Shahid , Matthew Wilcox , Mike Rapoport , Pankaj Gupta , Pasha Tatashin , Vipin Sharma , Vishal Annapurve , "Woodhouse, David" , linux-mm@kvack.org, kexec@lists.infradead.org Subject: Re: [Hypervisor Live Update] Notes from March 10, 2025 In-Reply-To: <20250320122303.GT9311@nvidia.com> References: <20250317172255.GO9311@nvidia.com> <755e80a2-60a7-4a04-9eb2-714e89ea34c5@app.fastmail.com> <20250320122303.GT9311@nvidia.com> Date: Wed, 26 Mar 2025 16:18:29 +0000 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: A5AFC1C0017 X-Stat-Signature: y6pgfefrt85wjrdgdk6nw93fdkcg3cxj X-Rspam-User: X-HE-Tag: 1743005914-317510 X-HE-Meta: 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 +cCCboAz xX8W8s8KmCLEN9/rNoOUikJTjVxY/vKZFJ0prAivhrzqGOAnOFnY8gRDJItvKVi0DMzESF+y1iCRlT+D3LuotHtZ3xLkF2y7yCNljYOX5G5vWiIRzQUc8diKMSn8c2JxvvKH89IyZ2xSGhaJVYFCsKrasQ1ZC44AF8d/zcTBmmhHnwZS3z2/xQiGWl1BMJ/Grp7Z9mki7BbxJHZkDGgZb3ArlVje6pK7MP7zJc2eZCFFdyvY73b/EJnLvWg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000012, 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, Mar 20 2025, Jason Gunthorpe wrote: >> I didn't mean the exact flags value, but the ability to have >> per-folio flags. The exact bits and their meaning would of course >> need to be part of the ABI. Shmem uses the dirty and uptodate flags >> to track some state on the folios, and the flags can affect it's >> behavior (lazily zeroing out falloc-ed pages for example). I am >> assuming other FD types or drivers might also want to store >> per-folio information. Having KHO core provide this facility can >> avoid duplicating the logic in each subsystem. > > For something simple like shmem I'd probably just suggest a side car bitmap > array or something? > > The trouble with trying to feed flags through the xarray thing is that > the memory holding that pfn data across the kexec is not itself > preserved memory so it is all blown away once the allocator starts. > > Any data that needs to be preserved further has to be copied into the > frozen struct page, which is pretty limiting in terms of what you > could preserve. A few bits could maybe work out but not alot of data. Right, that makes sense. I can live with a sidecar bitmap then. [...] -- Regards, Pratyush Yadav