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Howlett" Subject: Re: [PATCH] vfio: Request THP-aligned mmap for device fds Message-ID: References: <20260616180129.160016-1-anthony.pighin@nokia.com> <20260616163054.77fdb61a@shazbot.org> <20260617192928.GB231643@ziepe.ca> <160f8cdf-0d26-43f3-b487-4181e6374782@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <160f8cdf-0d26-43f3-b487-4181e6374782@arm.com> X-Stat-Signature: ntpwdqxkk33k88rwgzrr34g69jejxhp1 X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 8198A4000D X-HE-Tag: 1782143306-261814 X-HE-Meta: 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 ybu0qGRx lXknCbAxvzlNUf/glJnK12NG4CfjakuHj9fJY8MzrSp4PRnjgSzDefoO+Jr0wEEVrQX0LkhnHfAVnvm2iX+MmxBbkapV11byLcP/KPN77nGpvP8WoUI9cgBiXdwey1faFuWZd27iMG9xmOVqxP5k8LEi7BmXuiLg6tcRmrOiuy9Ll3+MT0aGaog+4ku9NlHg5HwAXeCqu6y3KrxOVRQt89/ybeK6cGVYPo1NHFpoXFgEUX/V1A66S3/HbrLUxX5CbMj3t Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jun 19, 2026 at 04:04:18PM +0100, Ryan Roberts wrote: > On 18/06/2026 15:55, Lorenzo Stoakes wrote: > > +cc Ryan for contPMD > > > >> > >>> And maybe there's a CONTPMD architecture we should also consider? > >> > >> ARM HW supports "CONTPMD" but I suppose it is not implemented.. > > > > Maybe Ryan has thoughts? > > Sorry not quite sure what you're asking so will give a generic answer: > > Arm arch does indeed support CONTPMD at level 2 in the same way that it supports > CONTPTE at level 3, as follows: > > +-----------+-----------+-----------+-----------+-----------+ > | Page Size | CONTPTE | PMD | CONTPMD | PUD | > +-----------+-----------+-----------+-----------+-----------+ > | 4KB | 64KB | 2MB | 32MB | 1GB | > | 16KB | 2MB | 32MB | 1GB | | > | 64KB | 2MB | 512MB | 16GB | | > +-----------+-----------+-----------+-----------+-----------+ > > For HugeTLB, Linux/arm64 support all of the listed sizes today. For !HugeTLB > (i.e. THP, large file filos) Linux/arm64 supports CONTPTE and PMD only. We could > (and probably would) extend to support CONTPMD once THP PUDs are supported. > > Not sure if that answers the question? Thanks, that's really useful! I think Jason's concern was that we'd have to account for contpmd here, but that'd only be w.r.t. THP rather than hugetlb, so we're safe for now I think! I guess this would be a new >PMD sized mTHP size which... I really hope we have the THP code in better shape once we come to that :) > > Thanks, > Ryan > > > > >> > >> Jason > > > > Thanks, Lorenzo > Cheers, Lorenzo