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The Go programming language
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Currently, we update memstats.heap_live from mcache.local_cachealloc whenever we lock the heap (e.g., to obtain a fresh span or to release an unused span). However, under the right circumstances, local_cachealloc can accumulate allocations up to the size of the *entire heap* without flushing them to heap_live. Specifically, since span allocations from an mcentral don't lock the heap, if a large number of pages are held in an mcentral and the application continues to use and free objects of that size class (e.g., the BinaryTree17 benchmark), local_cachealloc won't be flushed until the mcentral runs out of spans. This is a problem because, unlike many of the memory statistics that are purely informative, heap_live is used to determine when the garbage collector should start and how hard it should work. This commit eliminates local_cachealloc, instead atomically updating heap_live directly. To control contention, we do this only when obtaining a span from an mcentral. Furthermore, we make heap_live conservative: allocating a span assumes that all free slots in that span will be used and accounts for these when the span is allocated, *before* the objects themselves are. This is important because 1) this triggers the GC earlier than necessary rather than potentially too late and 2) this leads to a conservative GC rate rather than a GC rate that is potentially too low. Alternatively, we could have flushed local_cachealloc when it passed some threshold, but this would require determining a threshold and would cause heap_live to underestimate the true value rather than overestimate. Fixes #12199. name old time/op new time/op delta BinaryTree17-12 2.88s ± 4% 2.88s ± 1% ~ (p=0.470 n=19+19) Fannkuch11-12 2.48s ± 1% 2.48s ± 1% ~ (p=0.243 n=16+19) FmtFprintfEmpty-12 50.9ns ± 2% 50.7ns ± 1% ~ (p=0.238 n=15+14) FmtFprintfString-12 175ns ± 1% 171ns ± 1% -2.48% (p=0.000 n=18+18) FmtFprintfInt-12 159ns ± 1% 158ns ± 1% -0.78% (p=0.000 n=19+18) FmtFprintfIntInt-12 270ns ± 1% 265ns ± 2% -1.67% (p=0.000 n=18+18) FmtFprintfPrefixedInt-12 235ns ± 1% 234ns ± 0% ~ (p=0.362 n=18+19) FmtFprintfFloat-12 309ns ± 1% 308ns ± 1% -0.41% (p=0.001 n=18+19) FmtManyArgs-12 1.10µs ± 1% 1.08µs ± 0% -1.96% (p=0.000 n=19+18) GobDecode-12 7.81ms ± 1% 7.80ms ± 1% ~ (p=0.425 n=18+19) GobEncode-12 6.53ms ± 1% 6.53ms ± 1% ~ (p=0.817 n=19+19) Gzip-12 312ms ± 1% 312ms ± 2% ~ (p=0.967 n=19+20) Gunzip-12 42.0ms ± 1% 41.9ms ± 1% ~ (p=0.172 n=19+19) HTTPClientServer-12 63.7µs ± 1% 63.8µs ± 1% ~ (p=0.639 n=19+19) JSONEncode-12 16.4ms ± 1% 16.4ms ± 1% ~ (p=0.954 n=19+19) JSONDecode-12 58.5ms ± 1% 57.8ms ± 1% -1.27% (p=0.000 n=18+19) Mandelbrot200-12 3.86ms ± 1% 3.88ms ± 0% +0.44% (p=0.000 n=18+18) GoParse-12 3.67ms ± 2% 3.66ms ± 1% -0.52% (p=0.001 n=18+19) RegexpMatchEasy0_32-12 100ns ± 1% 100ns ± 0% ~ (p=0.257 n=19+18) RegexpMatchEasy0_1K-12 347ns ± 1% 347ns ± 1% ~ (p=0.527 n=18+18) RegexpMatchEasy1_32-12 83.7ns ± 2% 83.1ns ± 2% ~ (p=0.096 n=18+19) RegexpMatchEasy1_1K-12 509ns ± 1% 505ns ± 1% -0.75% (p=0.000 n=18+19) RegexpMatchMedium_32-12 130ns ± 2% 129ns ± 1% ~ (p=0.962 n=20+20) RegexpMatchMedium_1K-12 39.5µs ± 2% 39.4µs ± 1% ~ (p=0.376 n=20+19) RegexpMatchHard_32-12 2.04µs ± 0% 2.04µs ± 1% ~ (p=0.195 n=18+17) RegexpMatchHard_1K-12 61.4µs ± 1% 61.4µs ± 1% ~ (p=0.885 n=19+19) Revcomp-12 540ms ± 2% 542ms ± 4% ~ (p=0.552 n=19+17) Template-12 69.6ms ± 1% 71.2ms ± 1% +2.39% (p=0.000 n=20+20) TimeParse-12 357ns ± 1% 357ns ± 1% ~ (p=0.883 n=18+20) TimeFormat-12 379ns ± 1% 362ns ± 1% -4.53% (p=0.000 n=18+19) [Geo mean] 62.0µs 61.8µs -0.44% name old time/op new time/op delta XBenchGarbage-12 5.89ms ± 2% 5.81ms ± 2% -1.41% (p=0.000 n=19+18) Change-Id: I96b31cca6ae77c30693a891cff3fe663fa2447a0 Reviewed-on: https://go-review.googlesource.com/17748 Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Russ Cox <rsc@golang.org> |
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The Go Programming Language
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Binary Distribution Notes
If you have just untarred a binary Go distribution, you need to set the environment variable $GOROOT to the full path of the go directory (the one containing this file). You can omit the variable if you unpack it into /usr/local/go, or if you rebuild from sources by running all.bash (see doc/install-source.html). You should also add the Go binary directory $GOROOT/bin to your shell's path.
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See https://golang.org/doc/install or doc/install.html for more details.