Re: Memory again

[Dmitry Antipov]

On 11/26/2011 06:58 PM, Carsten Mattner wrote:

> Allow me to be naive and ask this: what about compaction?

Compaction implies the moving of live objects, which means that you
should be able to find _all_ pointers to such objects and update them.
Emacs GC has no such features, but it's technically possible
to enhance mark/sweep GC to do some heap compaction.

> Would the allocator in use fragment the overall system memory
> space if it frees more aggressively?

If you want to ask 'if we will run GC more often, will it reduce
heap fragmentation', the answer is most probably 'no'. You can try
to play with 'gc-cons-threshold' and 'gc-cons-percentage' and see
what happens. But, in general, heap fragmentation issues can't be
solved this way.

Other possible meanings of 'more aggressively' makes no sense for
simple (non-generational, non-incremental) mark/sweep GC since it
_always _ marks all live data and _always_ sweeps the whole
Lisp data regions of the heap.

If you're looking for good introduction to GC stuff, I would
recommend ftp://ftp.cs.utexas.edu/pub/garbage/gcsurvey.ps.

Dmitry