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Re: Locality problems caused by size based allocation?
- From: Jeff Sturm <jsturm at one-point dot com>
- To: Daniel Berlin <dberlin at dberlin dot org>
- Cc: gcc at gcc dot gnu dot org
- Date: Wed, 18 Dec 2002 00:00:54 -0500 (EST)
- Subject: Re: Locality problems caused by size based allocation?
On Tue, 17 Dec 2002, Daniel Berlin wrote:
> > What exactly is "size based allocation"?
> What ggc-page does, which is segregate objects based on size rather than
> age or object type.
Got it. But that puzzles me: the Boehm collector allocates one size
of object per heap block, fitting your desription of size-based
allocation, yet there was a measureable improvement over ggc-page?
> What version were you using?
Whatever was in the mainline GCC tree, probably 6.0.
> > Anyhow I didn't find the results interesting enough to continue the
> > experiment.
>
> Nor did I. It crashes in some of my testcases (we must be hiding pointers
> or something).
Yes, see my earlier example from cse.c. But the pointer hiding is easy to
avoid, once identified.
I was able to bootstrap GCC with boehm-gc, at one time.
> > that were happening you'd see plenty of blacklisted pointers (unless all
> > messages are suppressed, as with -DSILENT).
>
> You do.
> 100's of k worth.
Hmm... that's odd. Either your test cases exhibit very different behavior
than mine (I picked some of the larger sources in /gcc/) or your collector
is configured differently.
You'd see this if the heap blocks are intermixed with other mmap'ed
regions, for instance.
May I ask for your ggc-boehm patches (offline)?
Jeff