From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id D2207224E6913 for ; Thu, 1 Mar 2018 15:19:37 -0800 (PST) Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w21NNH3D087682 for ; Thu, 1 Mar 2018 18:25:46 -0500 Received: from e06smtp13.uk.ibm.com (e06smtp13.uk.ibm.com [195.75.94.109]) by mx0a-001b2d01.pphosted.com with ESMTP id 2gerprwn3k-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Thu, 01 Mar 2018 18:25:45 -0500 Received: from localhost by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 1 Mar 2018 23:25:42 -0000 Subject: Re: [PATCH v2 00/10] Copy Offload in NVMe Fabrics with P2P PCI Memory From: Benjamin Herrenschmidt Date: Fri, 02 Mar 2018 10:25:34 +1100 In-Reply-To: <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> <595acefb-18fc-e650-e172-bae271263c4c@deltatee.com> Mime-Version: 1.0 Message-Id: <1519946734.4592.48.camel@au1.ibm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: benh@au1.ibm.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" To: Logan Gunthorpe , Dan Williams Cc: Jens Axboe , linux-block@vger.kernel.org, Oliver OHalloran , linux-nvdimm , linux-rdma , linux-pci@vger.kernel.org, Linux Kernel Mailing List , linux-nvme@lists.infradead.org, Keith Busch , Alex Williamson , Jason Gunthorpe , =?ISO-8859-1?Q?J=E9r=F4me?= Glisse , Bjorn Helgaas , Max Gurtovoy , Christoph Hellwig List-ID: On Thu, 2018-03-01 at 16:19 -0700, Logan Gunthorpe wrote: > > 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 The big problem is not the vmemmap, it's the linear mapping. Cheers, Ben. _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm