linux-ext4 - Re: [PATCH RFC 00/10] RDMA/FS DAX truncate proposal

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Date:   Thu, 13 Jun 2019 12:12:18 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Theodore Ts'o <tytso@....edu>,
        Jeff Layton <jlayton@...nel.org>,
        Dave Chinner <david@...morbit.com>,
        Matthew Wilcox <willy@...radead.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH RFC 00/10] RDMA/FS DAX truncate proposal

On Wed, Jun 12, 2019 at 03:54:19PM -0700, Dan Williams wrote:
> > > My preference would be to avoid this scenario, but if it is really
> > > necessary, we could probably build it with some work.
> > >
> > > The only case we use it today is forced HW hot unplug, so it is rarely
> > > used and only for an 'emergency' like use case.
> >
> > I'd really like to avoid this as well.  I think it will be very confusing for
> > RDMA apps to have their context suddenly be invalid.  I think if we have a way
> > for admins to ID who is pinning a file the admin can take more appropriate
> > action on those processes.   Up to and including killing the process.
> 
> Can RDMA context invalidation, "device disassociate", be inflicted on
> a process from the outside? 

Yes, but it is currently only applied to the entire device - ie you do
'rmmod mlx5_ib' and all the running user space process see that their
FD has moved to some error and the device is broken.

Targetting the disassociate of only a single FD would be a new thing.

Jason