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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
Go is an open source programming language that makes it easy to build simple, reliable, and efficient software.
For documentation about how to install and use Go, visit https://golang.org/ or load doc/install-source.html in your web browser.
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Unless otherwise noted, the Go source files are distributed under the BSD-style license found in the LICENSE file.
--
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.
For example, if you extracted the tar file into $HOME/go, you might put the following in your .profile:
export GOROOT=$HOME/go
export PATH=$PATH:$GOROOT/bin
See https://golang.org/doc/install or doc/install.html for more details.