linux-kernel - Re: [PATCH] VFS: Add VFS event counter infrastructure

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Message-ID: <20110522022445.GU12317@one.firstfloor.org>
Date:	Sun, 22 May 2011 04:24:45 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
	npiggin@...nel.dk, tim.c.chen@...el.com
Subject: Re: [PATCH] VFS: Add VFS event counter infrastructure


Any comments on where I placed the counters?

> > This patch implements a simple per CPU counter framework for the VFS.
> > The counters are per CPU and are very little overhead. The counters
> > are output in debugfs (/sys/kernel/fs/vfsstat)
> 
> WTF?  Since when had debugfs become mandatory?

What do you mean? It's not mandatory of course.

I had it originally in /proc, but then moved it to debugfs.

> 
> > +	fs = debugfs_create_dir("fs", NULL);
> > +	if (fs)
> > +		debugfs_create_file("vfsstat", 0444, fs, NULL, &vfsstat_fops);
> > +	return 0;
> 
> Note that if that FPOS is configured away debugfs_create_dir() does _NOT_
> return NULL - you get ERR_PTR(-ENODEV).

That's fine because debugfs_create_file is a noop then too
and fs isn't used anywhere else.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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