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

Ingo Molnar
2010-10-18T18:20:00Z

* Eric Paris <eparis@redhat.com> wrote:

> On Mon, 2010-10-18 at 10:56 -0700, Linus Torvalds wrote:
> > On Mon, Oct 18, 2010 at 9:48 AM, Eric Paris <eparis@redhat.com> 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.
> >
> > Please. Look at the report more carefully.
> >
> > The radix tree memory use is disgusting. Yes. But it is absolutely NOT
> > sufficient to try to just fix that part. Go back, look at the original
> > report email, and this line in particular:
> >
> > 2235648 2069791 92% 0.12K 69864 32 279456K iint_cache
> >
> > There's 2.2 million iint_cache allocations too, each 128 bytes in
> > size. That's still a quarter _gigabyte_ of crap that adds zero value
> > at all.
>
> That was #2 in my list of things to fix:
>
> 2) IMA creates an entire integrity structure for every inode even when most or all
> of this structure will not be needed.
>
> I'm stating with #1 since that was 2G of wasted space (thus far my switch to
> rbtree seems to be surviving an xfstest) so I expect to send the patch this
> afternoon. #2 should attack the size of the iint_cache entries. #3 should attack
> the scalability. I'm certainly hoping I didn't miss part of the report....

I think it would be fair to argue that #2 is the thing that should be fixed first
and foremost - before touching any data structure details.

Because if you fix #2 then all the other items will become no-op to 99.9% of the
people who are affected by this bug today.

It's also probably a much simpler fix for -stable, so should be done first, etc.

If you do the data structure changes first then #2 will likely not be backportable
standalone and #1 will be risky to backport - creating nasty dependencies.

Thanks,

Ingo