Some GC stats

I invested some time making MIT/GNU Scheme compile itself with various sizes of heap. I did one set of runs with the variable compiler:preserve-data-structures? set to #f and another with it set to #t. The MIT/GNU Scheme compiler was written in a way that allows the garbage collector to reap the intermediate storage for the compiler after each phase of compilation. When compiler:preserve-data-structures? is set to #t, however, the intermediate data structures are retained until the next compilation. This should not change the total amount of storage used by the compiler, but it should have the effect of reducing the amount of storage recovered by a GC cycle. The number of GC cycles can be seen to be larger for the smaller heap sizes. When the heap is huge, the extra amount of storage in use has little effect on the GC count.

The Total Free column contains the sum of the memory freed after each GC totaled for the entire compilation.

Memory Size		Discard Data Structures		Preserve Data Structures
(blocks)	(words)	GC Count	Total Free	GC Count	Total Free
1890	1935360	3935	6213003931	-	-
1900	1945600	3882	6211940217	-	-
1920	1966080	3818	6213153480	-	-
2048	2097152	3502	6210260535	-	-
3072	3145728	2178	6205257571	-	-
4096	4194304	1589	6207697668	1626	6200942665
5000	5120000	1283	6206081325	1303	6198903924
6144	6291456	1033	6210675904	1043	6205324016
8192	8388608	766	6212253195	771	6207156928
16384	16777216	377	6222514645	379	6233468540
32768	33554432	188	6257358354	188	6244416384
40000	40960000	154	6266232939	154	6257300338
50000	51200000	124	6316240152	124	6311996423
65536	67108864	94	6283277196	94	6276744843
98304	100663296	63	6324424897	63	6320187112
131072	134217728	48	6430202774	48	6426705701
262144	268435456	25	6704242312	25	6702940561

Some of my thoughts about this (with graphs) in a bit. (It becomes very interesting when the data seriously disagrees with the math, but it is tedious to collect enough data to either support or refute the mathematical model.)