Hi, [EMAIL PROTECTED] (Ludovic Courtès) writes:
> * the heap gets more and more underutilized, although it seems to
> eventually stabilize somewhere around 5% (!) utilization (i.e.,
> total/alive = 20);
The main reason appears to be that the size of individual segments grows
exponentially (it's computed in `scm_i_get_new_heap_segment ()'). This
can be seen by regularly dumping the result of the following expression:
(map (lambda (elem)
(abs (- (cdr elem) (car elem))))
(assoc-ref (gc-stats) 'cell-heap-segments))
The default value of `scm_max_segment_size' is
`SCM_DEFAULT_MAX_SEGMENT_SIZE' and is as large as 20MiB (!). Setting it
to 64KiB, using the `GUILE_MAX_SEGMENT_SIZE' environment variable,
reduces the total heap size (not shown here) by a factor of 2, and
significantly improves the total-to-alive heap ratio:
<<inline: graph-64k.png>>
A side effect of using a smaller maximum segment size is that
`scm_i_adjust_min_yield ()' gets called more frequently (from
`scm_gc_for_newcell ()'), which explains the "smoother" increases of the
min yield.
Using the script I posted earlier, I get the following execution times
for 2500 iterations:
* max-segment-size = 64 KiB
real 3m1.167s
user 2m56.200s
sys 0m2.220s
* max-segment-size = 20 MiB
real 3m29.047s
user 3m22.392s
sys 0m4.764s
Thus it would be sensible to change `SCM_DEFAULT_MAX_SEGMENT_SIZE' to
some smaller value.
Thanks,
Ludovic.
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