linux-ext4 - Re: [PATCH v2] iomap: report collisions between directio and buffered writes to userspace

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Date:   Tue, 21 Nov 2017 04:52:53 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Dave Chinner <david@...morbit.com>
Cc:     "Darrick J. Wong" <darrick.wong@...cle.com>,
        xfs <linux-xfs@...r.kernel.org>,
        Ilya Dryomov <idryomov@...il.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Brian Foster <bfoster@...hat.com>,
        holger@...lied-asynchrony.com,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        linux-btrfs <linux-btrfs@...r.kernel.org>
Subject: Re: [PATCH v2] iomap: report collisions between directio and
 buffered writes to userspace

On Tue, Nov 21, 2017 at 05:48:15PM +1100, Dave Chinner wrote:
> On Mon, Nov 20, 2017 at 08:32:40PM -0800, Matthew Wilcox wrote:
> > On Mon, Nov 20, 2017 at 05:37:53PM -0800, Darrick J. Wong wrote:
> > > On Tue, Nov 21, 2017 at 09:27:49AM +1100, Dave Chinner wrote:
> > > > First thing I noticed was that "xa" as a prefix is already quite
> > > > widely used in XFS - it's shorthand for "XFS AIL". Indeed, xa_lock
> >
> > The X stands for 'eXpandable' or 'eXtending'.  I really don't want to
> > use more than a two-letter acronym for whatever the XArray ends up being
> > called.  One of the problems with the radix tree is that everything has
> > that 11-character 'radix_tree_' prefix; just replacing that with 'xa_'
> > makes a huge improvement to readability.
> 
> Yeah, understood. That's why
> we have very little clear
> prefix namespace left.... :/
> 
> [ somedays I write something that looks sorta like a haiku, and from
> that point on everything just starts falling out of my brain that
> way. I blame Eric for this today! :P ]

When the namespace is
tight we must consider the
competing users.

The earliest us'r
has a claim to a prefix
we are used to it.

Also a more wide-
spread user has a claim to
a shorter prefix.

Would you mind changing
your prefix to one only
one letter longer?

... ok, I give up ;-)

All your current usage of the xa_ prefix looks somewhat like this:

fs/xfs/xfs_trans_ail.c: spin_lock(&ailp->xa_lock);

with honourable mentions to:
fs/xfs/xfs_log.c:	spin_lock(&mp->m_ail->xa_lock);

Would you mind if I bolt a patch on to the front of the series called
something like "free up xa_ namespace" that renamed your xa_* to ail_*?
There are no uses of the 'ail_' prefix in the kernel today.

I don't think that
	spin_lock(&ailp->ail_lock);
loses any readability.

By the way, what does AIL stand for?  It'd be nice if it were spelled out
in at least one of the header files, maybe fs/xfs/xfs_trans_priv.h?

> Zoetrope Array.
> Labyrinth of illusion.
> Structure never ends.

Thank you for making me look up zoetrope ;-)