linux-kernel - Re: [PATCH rdma-next 01/10] RDMA: Add access flags to ib_alloc_mr() and ib_mr_pool

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Message-ID: <20210406123034.GA28930@lst.de>
Date:   Tue, 6 Apr 2021 14:30:34 +0200
From:   Christoph Hellwig <hch@....de>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Leon Romanovsky <leon@...nel.org>, Christoph Hellwig <hch@....de>,
        Bart Van Assche <bvanassche@....org>,
        Doug Ledford <dledford@...hat.com>,
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        Weihang Li <liweihang@...wei.com>,
        Yishai Hadas <yishaih@...dia.com>,
        Zhu Yanjun <zyjzyj2000@...il.com>
Subject: Re: [PATCH rdma-next 01/10] RDMA: Add access flags to
 ib_alloc_mr() and ib_mr_pool_init()

On Tue, Apr 06, 2021 at 09:13:12AM -0300, Jason Gunthorpe wrote:
> So we broadly have two choice
>  1) Diverge the kernel and user interfaces and make the RDMA drivers
>     special case all the kernel stuff to force
>     ACCESS_RELAXED_ORDERING when they are building MRs and processing
>     FMR WQE's
>  2) Keep the two interfaces the same and push the
>     ACCESS_RELAXED_ORDERING to a couple of places in the ULPs so the
>     drivers see a consistent API
> 
> They are both poor choices, but I think #2 has a greater chance of
> everyone doing their parts correctly.

No, 1 is the only sensible choice.  The userspace verbs interface is
a mess and should not inflict pain on the kernel in any way.  We've moved
away from a lot of the idiotic "Verbs API" concepts with things like
how we handle the global lkey, the new CQ API and the RDMA R/W
abstraction and that massively helped the kernel ecosystem.