Perl 6 - the future is here, just unevenly distributed

IRC log for #moarvm, 2016-03-08

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14:44 dalek MoarVM: 43edc3f | jnthn++ | src/ (2 files):
14:44 dalek MoarVM: Don't allocate second GC semi-space until needed.
14:44 dalek MoarVM:
14:44 dalek MoarVM: This knocks 4MB off threads that finish before they ever GC (including
14:44 dalek MoarVM: the main thread in programs that are single-threaded.)
14:44 dalek MoarVM: review: https://github.com/MoarVM/MoarVM/commit/43edc3faff
14:44 dalek MoarVM: 824748d | jnthn++ | src/ (5 files):
14:44 dalek MoarVM: Don't keep an MVMStaticFrame array in MVMCompUnit.
14:44 dalek MoarVM:
14:44 dalek MoarVM: We hardly ever did lookups in it, and could replace those few places
14:44 dalek MoarVM: that did with lookups via the coderefs array, just with an extra level
14:44 dalek MoarVM: of indirection. Saves 134KB off Rakudo base memory, plus a bit extra
14:49 arnsholt Oh, that first one is neat! Does it change startup time appreciably as well?
14:52 jnthn arnsholt: No; calloc is really quite cheap :)
14:53 jnthn And the second one doesn't also
14:55 arnsholt Yeah, I assumed that'd be the case. But allocations are one of those things that suddenly slow things down in some cases, so figured it'd be worth asking =)
14:56 jnthn massif says we go from a heap of 57,571,688 to a heap of 53,383,024 with those two patches, anyways.
14:57 jnthn For perl6 -e "say(1)"
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16:18 frwtv what is the advantage of having a smaller heap?
16:22 frwtv I'm almost sure that lazy allocation is already performed by the operating system
16:29 timotimo frwtv: why wouldn't it be good to not ask for as much space up front if it's not necessary?
16:29 timotimo the closer to "reality" the memory usage is, the more sensible decisions tools and admins can make about things
16:40 frwtv it depends, keeping a fixed value for the memory "cost" of a thread can also be a good in term of provisioning
16:40 frwtv a branch can cost a pipeline
16:40 timotimo if you have a thread that does most of its work with native values, for example, and you join() it before it does its first GC run, it won't ever cost the second semi-space
16:41 timotimo and as we gain escape analysis and start allocating our Scalars on the stack instead of the heap, and kick out unnecessary *LexRef/*AttrRef objects as well as temporary Int, Num or Str boxes at some point, we'll be getting much further without doing GC
16:42 timotimo in the future, it might happen that we make the semi space size tunable or even self-tuning
16:45 frwtv if in the future the people will start to use lot's of this kind of micro-thread (with auto-parallelization and such) then it makes sense
16:45 timotimo hm, i thought we'd probably be using a thread pool for that kind of thing, so threads would end up long-living after all
16:49 frwtv you might not need to run the GC for those threads
16:49 timotimo yes
16:49 timotimo after a time :)
16:50 timotimo but if i remember correctly we force a gc run when we join threads, too
16:50 timotimo in any case, we'll see about that when we get there
16:50 timotimo the patch itself is easy enough to revert
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