linux-kernel - Re: [PATCH v3 01/11] PCI/P2PDMA: Support peer-to-peer memory

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Date:   Thu, 15 Mar 2018 00:00:27 -0400
From:   "Martin K. Petersen" <martin.petersen@...cle.com>
To:     "Stephen Bates" <sbates@...thlin.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Sinan Kaya <okaya@...eaurora.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci\@vger.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-nvme\@lists.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-rdma\@vger.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-nvdimm\@lists.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-block\@vger.kernel.org" <linux-block@...r.kernel.org>,
        "Christoph Hellwig" <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH v3 01/11] PCI/P2PDMA: Support peer-to-peer memory


Stephen,

>> It would be useful if those configurations were not left behind so
>> that Linux could feasibly deploy offload code to a controller in the
>> PCI domain.
>    
> Agreed. I think this would be great. Kind of like the XCOPY framework
> that was proposed a while back for SCSI devices [1] but updated to also
> include NVMe devices. That is definitely a use case we would like this
> framework to support.

I'm on my umpteenth rewrite of the block/SCSI offload code. It is not as
protocol-agnostic as I would like in the block layer facing downwards.
It has proven quite hard to reconcile token-based and EXTENDED COPY
semantics along with the desire to support stacking. But from an
application/filesystem perspective everything looks the same regardless
of the intricacies of the device. Nothing is preventing us from
supporting other protocols...

-- 
Martin K. Petersen	Oracle Linux Engineering