linux-kernel - Re: [PATCH v2 00/22] Add new DMA mapping operation for P2PDMA

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Date:   Fri, 14 May 2021 10:30:25 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Christoph Hellwig <hch@....de>
Cc:     linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-block@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Stephen Bates <sbates@...thlin.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian König <christian.koenig@....com>,
        John Hubbard <jhubbard@...dia.com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jakowski Andrzej <andrzej.jakowski@...el.com>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v2 00/22] Add new DMA mapping operation for P2PDMA



On 2021-05-14 8:00 a.m., Christoph Hellwig wrote:
> On Thu, May 13, 2021 at 04:31:41PM -0600, Logan Gunthorpe wrote:
>>  17 files changed, 570 insertions(+), 290 deletions(-)
> 
> I'm a little worried about all this extra code for no new functionality
> at all.

Yes, this series is really just prep work for allowing new
functionality. And a bunch of cleanup has been tacked onto it. It should
make adding P2PDMA in userspace a lot easier and I expect other P2PDMA
use cases will be better enabled by it.

A lot of people don't like the pci_p2pdma_map_sg() special case and
can't use it in their use case because it only accepts homogenous SGLs.
This series gets rid of the special case and allows it to be used more
generally.

Logan