linux-kernel - Re: [Cluster-devel] [PATCH v6 10/19] gfs2: Introduce flag for glock holder auto-demotion

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Message-ID: <2508f12f0d2a5eedaad0c6b77657f53222b33e3c.camel@redhat.com>
Date:   Fri, 20 Aug 2021 14:41:32 +0100
From:   Steven Whitehouse <swhiteho@...hat.com>
To:     Bob Peterson <rpeterso@...hat.com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        "Darrick J. Wong" <djwong@...nel.org>
Cc:     Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>, cluster-devel@...hat.com,
        linux-fsdevel@...r.kernel.org, ocfs2-devel@....oracle.com
Subject: Re: [Cluster-devel] [PATCH v6 10/19] gfs2: Introduce flag for glock
 holder auto-demotion

Hi,

On Fri, 2021-08-20 at 08:11 -0500, Bob Peterson wrote:
> On 8/20/21 4:35 AM, Steven Whitehouse wrote:
> > Hi,
> > 
> > On Thu, 2021-08-19 at 21:40 +0200, Andreas Gruenbacher wrote:
> > > From: Bob Peterson <rpeterso@...hat.com>
> > > 
> > > This patch introduces a new HIF_MAY_DEMOTE flag and
> > > infrastructure
> > > that
> > > will allow glocks to be demoted automatically on locking
> > > conflicts.
> > > When a locking request comes in that isn't compatible with the
> > > locking
> > > state of a holder and that holder has the HIF_MAY_DEMOTE flag
> > > set,
> > > the
> > > holder will be demoted automatically before the incoming locking
> > > request
> > > is granted.
> > > 
> > I'm not sure I understand what is going on here. When there are
> > locking
> > conflicts we generate call backs and those result in glock
> > demotion.
> > There is no need for a flag to indicate that I think, since it is
> > the
> > default behaviour anyway. Or perhaps the explanation is just a bit
> > confusing...
> 
> I agree that the whole concept and explanation are confusing.
> Andreas 
> and I went through several heated arguments about the symantics, 
> comments, patch descriptions, etc. We played around with many
> different 
> flag name ideas, etc. We did not agree on the best way to describe
> the 
> whole concept. He didn't like my explanation and I didn't like his.
> So 
> yes, it is confusing.
> 
That seems to be a good reason to take a step back and look at this a
bit closer. If we are finding this confusing, then someone else looking
at it at a future date, who may not be steeped in GFS2 knowledge is
likely to find it almost impossible.

So at least the description needs some work here I think, to make it
much clearer what the overall aim is. It would be good to start with a
statement of the problem that it is trying to solve which Andreas has
hinted at in his reply just now,

Steve.