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Austin Clements 44078a3228 runtime: adjust huge page flags only on huge page granularity 
This fixes an issue where the runtime panics with "out of memory" or
"cannot allocate memory" even though there's ample memory by reducing
the number of memory mappings created by the memory allocator.

Commit 7e1b61c worked around issue #8832 where Linux's transparent
huge page support could dramatically increase the RSS of a Go process
by setting the MADV_NOHUGEPAGE flag on any regions of pages released
to the OS with MADV_DONTNEED. This had the side effect of also
increasing the number of VMAs (memory mappings) in a Go address space
because a separate VMA is needed for every region of the virtual
address space with different flags. Unfortunately, by default, Linux
limits the number of VMAs in an address space to 65530, and a large
heap can quickly reach this limit when the runtime starts scavenging
memory.

This commit dramatically reduces the number of VMAs. It does this
primarily by only adjusting the huge page flag at huge page
granularity. With this change, on amd64, even a pessimal heap that
alternates between MADV_NOHUGEPAGE and MADV_HUGEPAGE must reach 128GB
to reach the VMA limit. Because of this rounding to huge page
granularity, this change is also careful to leave large used and
unused regions huge page-enabled.

This change reduces the maximum number of VMAs during the runtime
benchmarks with GODEBUG=scavenge=1 from 692 to 49.

Fixes #12233.

Change-Id: Ic397776d042f20d53783a1cacf122e2e2db00584
Reviewed-on: https://go-review.googlesource.com/15191
Reviewed-by: Keith Randall <khr@golang.org>
2015-10-02 20:20:43 +00:00
api api: update go1.5.txt 2015-07-30 21:14:09 +00:00
doc doc: add text/template blocks and redefinition to go1.6.txt 2015-09-28 23:55:27 +00:00
lib/time lib/time: update to IANA release 2015e. 2015-07-22 02:56:31 +00:00
misc misc/cgo/testsanitizers: skip test for version of clang before 3.6 2015-10-02 14:17:33 +00:00
src runtime: adjust huge page flags only on huge page granularity 2015-10-02 20:20:43 +00:00
test cmd/compile: repair escape analysis of range &fixedArray 2015-10-01 18:49:18 +00:00
.gitattributes .gitattributes: prevent all magic line ending changes 2014-12-12 23:14:54 +00:00
.gitignore .gitignore: ignore y.output 2015-06-10 00:28:52 +00:00
AUTHORS A+C: automated updates 2015-09-10 00:59:04 +00:00
CONTRIBUTING.md doc: suggest security@golang.org for reporting security issues 2015-06-26 09:53:36 +00:00
CONTRIBUTORS A+C: automated updates 2015-09-10 00:59:04 +00:00
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README.md readme: emphasize issue tracker is for bugs/proposals 2015-10-02 18:44:14 +00:00
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README.md

The Go Programming Language

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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.