I posted this question on stackoverflow
(http://stackoverflow.com/questions/33780781/when-does-the-v8-gc-trigger-its-first-minor-gc-cycle-scavenge)
but I think I should have first posted it here. In any case, I'm confused
as to why V8 triggers 4 scavenges when I have only allocated one MB and
have explicitly set the min, max, and target new space to one MB. Now, I
can imagine that v8 might startup with some 'hidden' objects already on the
heap which might result in one scavenge being triggered before the user
code allocates a full MB, but it should still not result in 4 scavenges.
Either my math is wrong, or I'm missing something.
Here is the sample code that results in 4 GC cycles on the new space:
var BYTES_IN_MB = 1024 * 1024; // 1MB = 1024KB = 1024(KB/MB)*1024(B/KB)var
BYTES_IN_SMI = 4;var NUM_SMIS_IN_MB = BYTES_IN_MB/BYTES_IN_SMI;
var y = [];function allocateMB() {
for(var i = 0; i < NUM_SMIS_IN_MB; i++) {
y.push(i);
}}
allocateMB();
Here is the execution:
➜ ~ d8
V8 version 4.5.103.35 [console: readline]➜ ~ d8 --trace_gc --trace_gc_verbose
--min_semi_space_size=1 --max_semi_space_size=1 --target_semi_space_size=1
--semi_space_growth_factor=0 allocateMB.js[2853:0x7fa1fa012600] 6 ms:
Scavenge 1.7 (36.9) -> 1.2 (36.9) MB, 0.3 / 0 ms [allocation
failure].[2853:0x7fa1fa012600] Memory allocator, used: 37752 KB, available:
1461384 KB[2853:0x7fa1fa012600] New space, used: 281 KB, available:
726 KB, committed: 2015 KB[2853:0x7fa1fa012600] Old space, used:
674 KB, available: 0 KB, committed: 794 KB[2853:0x7fa1fa012600] Code
space, used: 194 KB, available: 0 KB, committed: 261
KB[2853:0x7fa1fa012600] Map space, used: 34 KB, available: 0
KB, committed: 59 KB[2853:0x7fa1fa012600] Large object space, used: 0
KB, available: 1460343 KB, committed: 0 KB[2853:0x7fa1fa012600] All
spaces, used: 1185 KB, available: 1461069 KB, committed: 3130
KB[2853:0x7fa1fa012600] External memory reported: 0
KB[2853:0x7fa1fa012600] Total time spent in GC : 0.3 ms[2853:0x7fa1fa012600]
7 ms: Scavenge 1.5 (36.9) -> 1.3 (36.9) MB, 0.4 / 0 ms [allocation
failure].[2853:0x7fa1fa012600] Memory allocator, used: 37752 KB, available:
1461384 KB[2853:0x7fa1fa012600] New space, used: 397 KB, available:
610 KB, committed: 2015 KB[2853:0x7fa1fa012600] Old space, used:
691 KB, available: 0 KB, committed: 794 KB[2853:0x7fa1fa012600] Code
space, used: 194 KB, available: 0 KB, committed: 261
KB[2853:0x7fa1fa012600] Map space, used: 34 KB, available: 0
KB, committed: 59 KB[2853:0x7fa1fa012600] Large object space, used: 0
KB, available: 1460343 KB, committed: 0 KB[2853:0x7fa1fa012600] All
spaces, used: 1317 KB, available: 1460954 KB, committed: 3130
KB[2853:0x7fa1fa012600] External memory reported: 0
KB[2853:0x7fa1fa012600] Total time spent in GC : 0.7 ms[2853:0x7fa1fa012600]
8 ms: Scavenge 1.9 (36.9) -> 1.5 (36.9) MB, 0.2 / 0 ms [allocation
failure].[2853:0x7fa1fa012600] Memory allocator, used: 37752 KB, available:
1461384 KB[2853:0x7fa1fa012600] New space, used: 596 KB, available:
411 KB, committed: 2015 KB[2853:0x7fa1fa012600] Old space, used:
691 KB, available: 0 KB, committed: 794 KB[2853:0x7fa1fa012600] Code
space, used: 194 KB, available: 0 KB, committed: 261
KB[2853:0x7fa1fa012600] Map space, used: 34 KB, available: 0
KB, committed: 59 KB[2853:0x7fa1fa012600] Large object space, used: 0
KB, available: 1460343 KB, committed: 0 KB[2853:0x7fa1fa012600] All
spaces, used: 1516 KB, available: 1460755 KB, committed: 3130
KB[2853:0x7fa1fa012600] External memory reported: 0
KB[2853:0x7fa1fa012600] Total time spent in GC : 0.9 ms[2853] Limited new
space size due to high promotion rate: 1 MB[2853:0x7fa1fa012600] 8 ms:
Scavenge 1.5 (36.9) -> 1.5 (37.9) MB, 0.7 / 0 ms [allocation
failure].[2853:0x7fa1fa012600] Memory allocator, used: 38776 KB, available:
1460360 KB[2853:0x7fa1fa012600] New space, used: 0 KB, available:
1007 KB, committed: 2015 KB[2853:0x7fa1fa012600] Old space, used:
1287 KB, available: 102 KB, committed: 1801 KB[2853:0x7fa1fa012600] Code
space, used: 194 KB, available: 0 KB, committed: 261
KB[2853:0x7fa1fa012600] Map space, used: 34 KB, available: 0
KB, committed: 59 KB[2853:0x7fa1fa012600] Large object space, used: 0
KB, available: 1459319 KB, committed: 0 KB[2853:0x7fa1fa012600] All
spaces, used: 1516 KB, available: 1460430 KB, committed: 4138
KB[2853:0x7fa1fa012600] External memory reported: 0
KB[2853:0x7fa1fa012600] Total time spent in GC : 1.6 ms
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