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

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Message-ID: <4CBC8C98.1090802@zytor.com>
Date:	Mon, 18 Oct 2010 11:06:16 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Eric Paris <eparis@...hat.com>
CC:	Kyle McMartin <kyle@...artin.ca>, James Morris <jmorris@...ei.org>,
	Christoph Hellwig <hch@...radead.org>,
	kernel@...ts.fedoraproject.org, Mimi Zohar <zohar@...ibm.com>,
	warthog9@...nel.org, Dave Chinner <david@...morbit.com>,
	linux-kernel@...r.kernel.org, Serge Hallyn <serue@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>, mingo@...e.hu
Subject: Re: ima: use of radix tree cache indexing == massive waste of memory?

On 10/18/2010 09:48 AM, Eric Paris wrote:
> 
> 1) IMA uses radix trees which end up wasting 500 bytes per inode because
> the key is too sparse.  I've got a patch which uses an rbtree instead
> I'm testing and will send along shortly.  I found it funny working on
> the patch to see that Documentation/rbtree.txt says "This differs from
> radix trees (which are used to efficiently store sparse arrays and thus
> use long integer indexes to insert/access/delete nodes)"  Which flys in
> the face of this report.
> 

Radix trees can efficiently store data associated with sparse keys *as
long as the keys are clustered*.  For random key distributions, they
perform horribly.

	-hpa
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