d19fedd180
Currently, the GC stores the object marks for checkmarks mode in the heap bitmap using a rather complex encoding: for one word objects, the checkmark is stored in the pointer/scalar bit since one word objects must be pointers; for larger objects, the checkmark is stored in what would be the scan/dead bit for the second word of the object. This encoding made more sense when the runtime used the first scan/dead bit as the regular mark bit, but we moved away from that long ago. This encoding and overloading of the heap bitmap bits causes a great deal of complexity in many parts of the allocator and garbage collector and leads to some subtle bugs like #15903. This CL moves the checkmarks mark bits into their own per-arena bitmap and reclaims the second scan/dead bit as a regular scan/dead bit. I tested this by enabling doubleCheck mode in heapBitsSetType and running in both regular and GODEBUG=gccheckmark=1 mode. Fixes #15903. No performance degradation. (Very slight improvement on a few benchmarks, but it's probably just noise.) name old time/op new time/op delta BiogoIgor 16.6s ± 1% 16.4s ± 1% -0.94% (p=0.000 n=25+24) BiogoKrishna 19.2s ± 3% 19.2s ± 3% ~ (p=0.638 n=23+25) BleveIndexBatch100 6.12s ± 5% 6.17s ± 4% ~ (p=0.170 n=25+25) CompileTemplate 206ms ± 1% 205ms ± 1% -0.43% (p=0.005 n=24+24) CompileUnicode 82.2ms ± 2% 81.5ms ± 2% -0.95% (p=0.001 n=22+22) CompileGoTypes 755ms ± 3% 754ms ± 4% ~ (p=0.715 n=25+25) CompileCompiler 3.73s ± 1% 3.73s ± 1% ~ (p=0.445 n=25+24) CompileSSA 8.67s ± 1% 8.66s ± 1% ~ (p=0.836 n=24+22) CompileFlate 134ms ± 2% 133ms ± 1% -0.66% (p=0.001 n=24+23) CompileGoParser 164ms ± 1% 163ms ± 1% -0.85% (p=0.000 n=24+24) CompileReflect 466ms ± 5% 466ms ± 3% ~ (p=0.863 n=25+25) CompileTar 182ms ± 1% 182ms ± 1% -0.31% (p=0.048 n=24+24) CompileXML 249ms ± 1% 248ms ± 1% -0.32% (p=0.031 n=21+25) CompileStdCmd 10.3s ± 1% 10.3s ± 1% ~ (p=0.459 n=23+23) FoglemanFauxGLRenderRotateBoat 8.66s ± 1% 8.62s ± 1% -0.47% (p=0.000 n=23+24) FoglemanPathTraceRenderGopherIter1 20.3s ± 3% 20.2s ± 2% ~ (p=0.893 n=25+25) GopherLuaKNucleotide 29.7s ± 1% 29.8s ± 2% ~ (p=0.421 n=24+25) MarkdownRenderXHTML 246ms ± 1% 247ms ± 1% ~ (p=0.558 n=25+24) Tile38WithinCircle100kmRequest 779µs ± 4% 779µs ± 3% ~ (p=0.954 n=25+25) Tile38IntersectsCircle100kmRequest 1.02ms ± 3% 1.01ms ± 4% ~ (p=0.658 n=25+25) Tile38KNearestLimit100Request 984µs ± 4% 986µs ± 4% ~ (p=0.627 n=24+25) [Geo mean] 552ms 551ms -0.19% https://perf.golang.org/search?q=upload:20200723.6 Change-Id: Ic703f26a83fb034941dc6f4788fc997d56890dec Reviewed-on: https://go-review.googlesource.com/c/go/+/244539 Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Michael Knyszek <mknyszek@google.com> Reviewed-by: Martin Möhrmann <moehrmann@google.com> |
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