linux-kernel - Re: [PATCH 0/7] Eliminate delegation self-conflicts

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Message-ID: <20190211155803.GA28714@parsley.fieldses.org>
Date:   Mon, 11 Feb 2019 10:58:04 -0500
From:   "J. Bruce Fields" <bfields@...hat.com>
To:     Jeff Layton <jlayton@...hat.com>
Cc:     linux-nfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Trond Myklebust <trondmy@...merspace.com>,
        David Howells <dhowells@...hat.com>, Tejun Heo <tj@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Shaohua Li <shli@...com>, Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 0/7] Eliminate delegation self-conflicts

On Sat, Feb 09, 2019 at 07:43:54AM -0500, Jeff Layton wrote:
> On Fri, 2019-02-08 at 15:10 -0500, J. Bruce Fields wrote:
> > From: "J. Bruce Fields" <bfields@...hat.com>
> > 
> > These patches allow NFSv4 clients holding delegations to keep them when
> > the operation that would break a delegation comes from the same client.
> > 
> > To do that, we somehow need to pass the identity of the
> > delegation-breaker down through the VFS.
> > 
> > This series uses the tgid, a solution suggested by Trond.  To do that we
> > need nfsd tasks to share the same tgid.  I do that by extending the
> > kthread code slightly to allow knfsd to run the kthreadd main loop in a
> > task of its own, and spawn its server threads off of that task.
...
> Nice work! I like the basic idea, the changes seem to be well-organized, 
> and the tgid semantics are clear and make sense.
> 
> Would this preclude us from moving to a workqueue-based model for knfsd
> later? It's likely to still be worth it, but it'd be good to understand
> the potential drawbacks.

I was wondering about that too, but I haven't looked into it yet.
Workqueues look a lot more complicated than kthreads.

--b.