From mboxrd@z Thu Jan 1 00:00:00 1970 From: Logan Gunthorpe Subject: Re: [PATCH v2 00/10] Copy Offload in NVMe Fabrics with P2P PCI Memory Date: Thu, 1 Mar 2018 16:19:59 -0700 Message-ID: <595acefb-18fc-e650-e172-bae271263c4c@deltatee.com> References: <20180228234006.21093-1-logang@deltatee.com> <1519876489.4592.3.camel@kernel.crashing.org> <1519876569.4592.4.camel@au1.ibm.com> <1519936477.4592.23.camel@au1.ibm.com> <2079ba48-5ae5-5b44-cce1-8175712dd395@deltatee.com> <43ba615f-a6e1-9444-65e1-494169cb415d@deltatee.com> <1519945204.4592.45.camel@au1.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1519945204.4592.45.camel-8fk3Idey6ehBDgjK7y7TUQ@public.gmane.org> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" To: benh-8fk3Idey6ehBDgjK7y7TUQ@public.gmane.org, Dan Williams Cc: Jens Axboe , linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Oliver OHalloran , linux-nvdimm , linux-rdma , linux-pci-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Linux Kernel Mailing List , linux-nvme-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Keith Busch , Alex Williamson , Jason Gunthorpe , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Bjorn Helgaas , Max Gurtovoy , Christoph Hellwig List-Id: linux-rdma@vger.kernel.org On 01/03/18 04:00 PM, Benjamin Herrenschmidt wrote: > We use only 52 in practice but yes. > >> That's 64PB. If you use need >> a sparse vmemmap for the entire space it will take 16TB which leaves you >> with 63.98PB of address space left. (Similar calculations for other >> numbers of address bits.) > > We only have 52 bits of virtual space for the kernel with the radix > MMU. Ok, assuming you only have 52 bits of physical address space: the sparse vmemmap takes 1TB and you're left with 3.9PB of address space for other things. So, again, why doesn't that work? Is my math wrong? Logan