Mutator creates an array of mps_gen_param_s structs (for example: [ { 100KB, 90% mortality }, { 100K, 50% mortality } ] ), passes it to mps_chain_create, and uses this chain to create a new AMC pool.
+Say the mutator creates an array of 2 mps_gen_param_s structs:
+The Chain contains an array of two GenDescs: numbers 0 and 1. The AMC pool creates *three* PoolGens: 0 and 1 are linked to the corresponding GenDesc, and 2 is linked to the arena-wide "topGen" GenDesc.
+It passes this array to mps_chain_create, and then uses the chain to create a new AMC pool.
-The GenDesc zonesets are empty. The PoolGen newSizes are zero.
+The Chain contains an array of two GenDescs: numbers 0 and 1. The AMC pool creates *three* PoolGens:
+The PoolGen newSizes are zero. The GenDesc zonesets are empty.
Mutator creates and uses an allocation buffer, making new objects accumulate in the nursery generation.
-When AMCBufferFill asks for new memory segments, it passes the PoolGen's "nr" generation number (0 for mutator allocation, 1 or 2 for preserved objects) as a segment-placement preference (with SegPrefGen).
+ +ArenaVM tries hard to keep all segments for this SegPrefGen-number together in the same zone or zones, and separate from the zones used for all other things. (Such as: zones with other generations, blacklist zones, and as-yet unused zones).
+ + +AMCBufferFill does this accounting: + +
The segment's size is added into the PoolGen's newSize.
+ +The segment's zoneset is unioned into the GenDesc zoneset (by calling PoolGenUpdateZones).
+ + +All collections start from ArenaStep(). There are two routes into ArenaStep: an explicit call to mps_arena_step(), or an implicit one from the time-stealing ArenaPolls in mps_alloc, mps_reserve, and mps_alloc_pattern_end/reset.
+ + +There are two trigger conditions:
+ +Firstly, lots of "spare time". An explicit call to mps_arena_step() can specify non-zero interval and multiplier. If (interval x multiplier) is big enough, and it's been long enough since the last one, start a full collection.
+ +Secondly (when ArenaStep calls TracePoll) the infamous "dynamic criterion". The plan is to start a full collection soon enough so that we don't completely run out of memory. I hope that the idea of this is:
+ +Both trigger conditions call traceStartCollectAll().
+ + +traceStartCollectAll() finds all chains, all the PoolGens in Gen 0 of those chains, all the pools those PoolGens are part of, all the segments of those pools, and condemns all those segments:
+ +traceStartCollectAll(): + traceCondemnAll() + for chain in all chains: + ChainCondemnAll(chain)+ +
ChainCondemnAll(chain): + for PoolGen in GenDesc 0 of chain: + for Seg in (PoolGen->pool)->SegRing: + TraceWhiten(Seg)+ +
Note that AMS pools have a Gen-0-only chain (and so get condemned).
+ +Note that LO and AWL pools also have a Gen-0-only chain (and so get condemned). [This is despite their segment-placement preference being hardwired to SegPrefGen-number 1; yuk! RHSK 2006-12-01]
A minor collection is triggered if there's a chain whose GenDesc 0 is 'over capacity': the sum of the PoolGen 0 newSizes exceeds the GenDesc's capacity. (If there's a choice, pick the chain whose Gen 0 is most over capacity).
+ +[Note that we only look at "newSize". I don't understand what this means, or how it differs from totalSize. (It may be a consequence of nailing, perhaps?). RHSK 2006-12-01]
+ + +For the triggering chain, ChainCondemnAuto() finds the list of GenDescs to condemn: GenDesc 0 and each higher GenDesc that's also over its capacity. (That is: where the sum of newSizes exceeds capacity, as before).
+ +These GenDescs have been recording the zoneset of all the segments ever added into that GenDesc, as long as the pool noted it by calling PoolGenUpdateZones(PoolGen, Seg).
+ +ChainCondemnAuto() calls TraceCondemnZones() to condemn the full zoneset ever touched by any segment in any of the condemned GenDescs.
+ +TraceCondemnZones() uses the SegFirst/SegNext() iterator, and for every segment that is wholly within the condemned zones, it calls TraceAddWhite(seg).
+ +2006-11-30 RHSK Created, incomplete. + 2006-12-01 RHSK What triggers a GC?