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    SubjectRe: ima: use of radix tree cache indexing == massive waste of memory?
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    On Mon, 2010-10-18 at 20:19 +0200, Ingo Molnar wrote:
    > * 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.

    Good point. I'll keep that in mind and possibly reorder.

    -Eric



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