My previous attempts to improve method table (mt_tbl) performance by introducing a load factor and adjusting the initial allocation size unfortunately led to undesirable increases in memory consumption.
Given that memory usage is a primary concern, I've reverted the following changes:
- Removed the load factor based rehashing logic.
- Removed the related definitions for the load factor.
- Ensured the initial allocation size is 8.
This restores the method table to its original behavior, where it rehashes only when the table is completely full or during initial allocation. This should bring memory usage back to its baseline level prior to these optimization attempts.
The method table (mt_tbl) in src/class.c previously only rehashed when it became completely full. With linear probing, this could lead to significant performance degradation for lookups and insertions as the table approached full capacity.
This change introduces a load factor (MT_LOAD_FACTOR_NUM/MT_LOAD_FACTOR_DEN, set to 3/4 or 0.75). The mt_put function now checks if adding a new element would cause the table's size to meet or exceed this load factor relative to its allocated capacity. If so, it triggers a rehash before inserting the new element.
This helps maintain more empty slots in the hash table, improving the average-case performance of linear probing and reducing the likelihood of worst-case scenarios. The existing initial allocation size and doubling strategy for rehashing are retained.
ADDI/SUBI may fall back to method call that may clear block argument
place holder, which may be a live register. So we cannot directly call
ADDI/SUBI over local variables.
Since we have introduced lrama, everyone can generate same `y.tab.c`
on any platform, without installing Bison. That was the reason we have
removed `y.tab.c` from the repository. But this change cause #6515 and
bothered out-of-tree builds. So we (reluctantly) added `y.tab.c` again.
mempool.h provide compatibility layer so that existing programs does not
need to update (but update recommended anyway, since compatibility layer
takes mrb_state that is not used at all).
Since mrb_calloc() (along with mrb_calloc) takes two arguments: nmemb
which is number of array elements, and size which is size of the array.
Of course, revsersing does not change the behavior, but we'd like to
respect the original design intention of calloc(3).
Yukihiro "Matz" Matsumoto