linux-kernel - Re: [PATCH] vfs: Add a trace point in the mark_inode

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Message-ID: <20091120105154.GB12634@elte.hu>
Date:	Fri, 20 Nov 2009 11:51:54 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	"Kok, Auke" <auke-jan.h.kok@...el.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Jeff Garzik <jeff@...zik.org>,
	"Wu, Fengguang" <fengguang.wu@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Al Viro <viro@...IV.linux.org.uk>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH] vfs: Add a trace point in the mark_inode_dirty function


* Christoph Hellwig <hch@...radead.org> wrote:

> Guys, I think both the inode number and name do have a use case.  For 
> file system developers observing the filesystem the inode number is 
> very useful, and if you look at the ext4 tracing already in tree or 
> the xfs tracing going in in the next window they use the inode number 
> all over.
> 
> Which btw brings up another good argument - to make the tracing really 
> useful we need to have conventions.  While the inode number seems to 
> be a realtively easy one printing the device is more difficult.  XFS 
> just prints the raw major/minor to stay simple, ext4 has a complicated 
> ad-hoc cache of device names, and this one just prints the superblock 
> id string.

Agreed.

> Of course for a user the name is a lot more meaninful, but also 
> relatively expensive to generate.  Then again I'm not even sure how 
> the last pathname component only here is all that useful - it can't be 
> used to easily find the file.

That's not the main point though - the point is for app developers (and 
users) being able to see 'oh, _that_ file it is, we need to fix that'. 
In the context of a specific app, the last component filename carries 
95% of the useful information.

Look at how PowerTOP does it, for a real-life usecase.

	Ingo
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