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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Peter Xu , Alex Williamson , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/huge_memory: allow huge pfnmaps regardless of THP mode Message-ID: References: <20260821070520.25759-1-saravanand@crusoe.ai> <20260821193220.91799-1-saravanand@crusoe.ai> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260821193220.91799-1-saravanand@crusoe.ai> X-Rspam-User: X-Rspamd-Queue-Id: BDA5A1C0005 X-Rspamd-Server: rspam07 X-Stat-Signature: 1tna7g61i3exht198h78rh3jpq1buyst X-HE-Tag: 1787408994-353438 X-HE-Meta: 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 qOMXsfQS b9RDagQwXjCIyqWLyJM5t4fo+rDCRypgpk45ng+armvytasm1Qsfpf6kXCauRaBoV8d/9iubT9Till4UBHyD0/hjIE2u6xo51ry8XTrov0uBiK/MBwHwRad7TUnXNxZ2ui3I5YL/C1goRfdkiA6nL14exkleykoHqVaPHnvT9C0c3lI3ihrHRAcm3oSH8d4I3b86LrjO24pGEZbcB6FHvqWEoBsIYM5D8r20e5HiLlCkTu5mUTM7GFUTaFbcLif3tvRW7tWTM/nujmkGaPA50AxH5o07fdhiVc2/yqXqfkf29G7aaQWTIBBCaHktn7Gyae0pv2da2DLMmJKk3q3L2aATWihvzRgj+2h/1 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Aug 21, 2026 at 12:32:20PM -0700, Saravanan D wrote: > On Fri, Aug 21, 2026 at 09:03:15AM +0100, Lorenzo Stoakes (ARM) wrote: > > In any case if you'd taken 5 minutes to search the mailing list you'd see > > this was: > > > > a. Already submitted (so your patch reads like plagiarism). > > b. Already rejected in favour of me doing an actually sensible solution. > > > > https://lore.kernel.org/linux-mm/anL-NZkNMSSxN0YN@lucifer/ > > Apologies and please disregard my patch. I had not > searched the list before sending and was unaware of Cédric's patch > and your rework. Mine came from an independent observation of slow > VM boot times on Ubuntu based hosts running cloud-hypervisor with H100 > GPUs. The patch was prepared with AI assistance and should have > carried an Assisted-by tag. All of my future submissions will. > > I backported the diff you attached in your earlier response to > a 6.17 based kernel and ran it on a HGX host with four H100 GPUs, > each exposing a 128 GiB BAR1, with cloud-hypervisor. THP > mode was the Ubuntu default - madvise in all runs. > > VFIO_IOMMU_MAP_DMA 4 GPU VM boot > per 128 GiB BAR > 6.17 unpatched 20.7s 97s > 6.17 + your diff 0.4s 17s > > Each BAR mapped with 128 PUD faults. Your approach will definitely > improve VM boot times in our production. Very grateful for your > contribution. Thanks, always appreciate real world data :) I will send the actual patch at some point it's on my never ending TODO list... :) > > Thanks, > Saravanan D. -- Cheers, Lorenzo