JavaScript:SpiderMonkey:Arena Allocation
The SpiderMonkey arena allocation API is used for:
- Stack space in the JSContext (to be removed by bug 540706)
- Temp space in the JSContext
- Bytecodes/source notes in the js::Compiler for expanding compilation storage
- JSScopeProperties in the JSPropertyTree objects
- Temp space for regular expression matching, stored in the JSContext
- Decompiler printer objects
Plans
| Name | Size (weeks) |
|---|---|
| Soft release | 1 |
| Chunk policy | 0.5 |
Time-deferred "soft" release — it was observed in the execution of imacro_asm.js that the regexp pool thrashes quite a bit: a recurring free/alloc of a single arena occurs with each simple regular expression match. By sticking a timestamp on the arena pool and having the garbage collector release the outstanding arenas at a later time we can avoid this overhead in the common case.
Determine optimal arena chunk policy — the arena chunk sizes should mesh with the virtual memory subsystem as nicely as possible. For example, mallocing PAGE_SIZE + 1 byte is probably not ideal. It appears that OS X and Linux follow the same allocation patterns with their malloc implementations WRT their page sizes from these experiments. Further investigation would probably be helpful in determining an overall policy. References: 421435, 561286
