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

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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>,
        Avihai Horon <avihaih@...dia.com>,
        Adit Ranadive <aditr@...are.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Ariel Elior <aelior@...vell.com>,
        Bernard Metzler <bmt@...ich.ibm.com>,
        Chuck Lever <chuck.lever@...cle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        Devesh Sharma <devesh.sharma@...adcom.com>,
        Faisal Latif <faisal.latif@...el.com>,
        Jack Wang <jinpu.wang@...os.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Jens Axboe <axboe@...com>,
        Karsten Graul <kgraul@...ux.ibm.com>,
        Keith Busch <kbusch@...nel.org>, Lijun Ou <oulijun@...wei.com>,
        linux-cifs@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-rdma@...r.kernel.org, linux-s390@...r.kernel.org,
        Max Gurtovoy <maxg@...lanox.com>,
        Max Gurtovoy <mgurtovoy@...dia.com>,
        "Md. Haris Iqbal" <haris.iqbal@...os.com>,
        Michael Guralnik <michaelgur@...dia.com>,
        Michal Kalderon <mkalderon@...vell.com>,
        Mike Marciniszyn <mike.marciniszyn@...nelisnetworks.com>,
        Naresh Kumar PBS <nareshkumar.pbs@...adcom.com>,
        netdev@...r.kernel.org, Potnuri Bharat Teja <bharat@...lsio.com>,
        rds-devel@....oracle.com, Sagi Grimberg <sagi@...mberg.me>,
        samba-technical@...ts.samba.org,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        Selvin Xavier <selvin.xavier@...adcom.com>,
        Shiraz Saleem <shiraz.saleem@...el.com>,
        Somnath Kotur <somnath.kotur@...adcom.com>,
        Sriharsha Basavapatna <sriharsha.basavapatna@...adcom.com>,
        Steve French <sfrench@...ba.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        VMware PV-Drivers <pv-drivers@...are.com>,
        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.