linux-kernel - Re: ima: use of radix tree cache indexing == massive waste of memory?

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Date:	Sun, 17 Oct 2010 14:52:03 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Eric Paris <eparis@...isplace.org>, eparis@...hat.com,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Dave Chinner <david@...morbit.com>,
	linux-kernel@...r.kernel.org, Mimi Zohar <zohar@...ibm.com>,
	warthog9@...nel.org, hpa@...or.com, devel@...ts.fedoraprojet.org
Subject: Re: ima: use of radix tree cache indexing == massive waste of memory?

On Sun, Oct 17, 2010 at 03:59:20PM +0200, Peter Zijlstra wrote:
> Well, it does suck it needs to bloat data and code when its effectively
> disabled. Isn't there a way to gather this data before we enable it, eg.
> scan the files list on enable or somesuch?
> 
> I mean, if you mandate an external storage you might as well extend
> struct inode, that's cheaper in each respect.

That's in fact what it did initially.  While IBM claimed it would never
be enabled in distros and this would be fine I feared this would not be
true and told them to not make it have overhead if compiled in but not
used.

Turns out I wa right in my fear that IBM pressured distros to enable
it anyway.  And turns out that I should have verified they didn't
actually mess it up instead of expecting people to get such trivial
things right.

> Me, I'm henceforth making sure to have CONFIG_IMA disabled...

Yeah.

> >  but it doesn't
> > help the fact that the suggested structure for storage (the radix
> > tree) is apparently quite inefficient.  I'd love to hear other
> > suggestions for a better structure.... 
> 
> radix tree is efficient for dense sets, not sparse sets.

Which actually works just fine for inodes on many filesystems if you
use the right key.
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