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t=1785947391; bh=q9L2N9YRxda5Bh032maEDALi7aTeAmsvta3X79RfQpo=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=U/g+aw9Z6Bn8DJHf76ODlG6+nfC79yTIBLBiI6tvVxfuoykLHCMXCju2F8BwJHTU6 pj9UX58lBg8TJ+DraHlbBlPtclIhJtbxPvzUBHuBXROx/CSCt+dSsx1EDsW/z7WTu1 nD2XAYmaxsP2aOkXPgGsC31tRHp8vNRdgkDAD4xbGutpCPeSVzHxghNp/nNbBL6ifw x8Qi8jlSJCm3ixVH4WyTDgoQOIW9CRkQ44/qjSzCa/uKz+oGJpWyMYZrl2E6DUQd2X FjOE/7kO/lFz75YYlxRutFq+mhqiFdmnKBIb3ooCR9wyBEoYVCKqZWOydYGIye4S/h i4bxMBl/smNzw== Date: Wed, 5 Aug 2026 17:29:34 +0100 From: "Lorenzo Stoakes (ARM)" To: Jason Gunthorpe Cc: =?utf-8?Q?C=C3=A9dric?= Le Goater , Andrew Morton , linux-mm@kvack.org, Peter Xu , David Hildenbrand , Alex Williamson , Zi Yan , stable@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/huge_memory: let special huge VMAs bypass the THP policy check Message-ID: References: <20260805055544.1568534-1-clg@redhat.com> <20260805121524.GM27883@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260805121524.GM27883@nvidia.com> X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 201DA1C000B X-Stat-Signature: 9itttt5ntuu1ozkofgj5w48a3hh91m9i X-Rspam-User: X-HE-Tag: 1785947391-987097 X-HE-Meta: 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 TFIu56mQ 03h8Pwa0z0GtghJQMvsbgHRB56f0E8PbqxIlScqUqSAF2JeUb3iT6zVg+geq9xj96Ma8etAU3BA/5Lox7aMO2L+maYKZTzHsJ23lpdGQtcXynfNWCB3FXhuSPV4gFhHQVLTHqIhC9qx3zuo+EJr7oqI/XOhnxrM2IAJoee3NZzu/WVEzDOcnqYiyCenutOtj33py6AxTrtNPHlKxTKVR6AuZZM/UPn/Jjld3zrFi2eZgKcjvn3/8vEQRVKnk+/te4REaLja6cavd/jHCcjvWunUNWQciNztMg3ygahAReqhuIMmVInP8mHPDiYxOiTfVGo6ngC1ifbRPxKi6UFnQVHRQEwkNLMVFWM35g Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Aug 05, 2026 at 09:15:24AM -0300, Jason Gunthorpe wrote: > On Wed, Aug 05, 2026 at 07:55:40AM +0200, Cédric Le Goater wrote: > > > The result: each 256 GB BAR is mapped at 4 KiB granularity -- 67 million > > page faults per GPU instead of a few thousand PMD/PUD faults. On hosts > > with 8 GPUs (2 TB of BAR space), this causes VM boot times to degrade > > severely, with 99.98% of CPU time spent in the VFIO BAR mapping path. > > Broadly upstream we expect people to use iommufd and dmabuf for these > configurations to avoid all this nonsense overhead. :\ Point taken on that :) but I think it's generally reasonable in line with the huge PFN map changes to do something like I suggested. > > Jason -- Cheers, Lorenzo