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runtime: provide way to disable MADV_FREE #28466

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aclements opened this issue Oct 29, 2018 · 3 comments
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runtime: provide way to disable MADV_FREE #28466

aclements opened this issue Oct 29, 2018 · 3 comments
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FrozenDueToAge release-blocker
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Go1.12

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@aclements
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aclements commented Oct 29, 2018 •
edited by cespare

CL 135395 switched from MADV_DONTNEED to MADV_FREE for releasing physical memory on Linux. MADV_FREE has many performance advantages, but seems to have one downside: because it releases pages lazily, it doesn't reduce a process's RSS until the system is actually under memory pressure.

I'm concerned that this may be confusing to users, but more concerned that this may confuse automated systems that monitor RSS and/or container memory usage, particularly if those systems make decisions based on this.

We may want to provide a GODEBUG setting to fall back to MADV_DONTNEED. This will give us/users a low-overhead way to confirm if this is causing a user issue as well as a workaround if it is. And then we can collect information on problems caused by this. If they're minor, we can take this GODEBUG out in the future. If they're major, we can roll this back.

/cc @mknyszek @RLH
@aclements aclements added this to the Go1.12 milestone Oct 29, 2018
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As a way to experiment with MADV_DONTNEED and MADV_FREE, I created a test program.

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Change https://golang.org/cl/155931 mentions this issue: runtime: add GODEBUG=madvdontneed=1

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Change https://golang.org/cl/155929 mentions this issue: doc/go1.12: mention Conn.SetDeadline improvements, GODEBUG=madvdontneed=1

gopherbot pushed a commit that referenced this issue Jan 4, 2019
@bradfitz
doc/go1.12: mention Conn.SetDeadline improvements, GODEBUG=madvdontne…
d15ffca 
…ed=1

Fixes #29439
Updates #28466

Change-Id: Ifa0779a089a969f99f1a47127e23565f31eec24f
Reviewed-on: https://go-review.googlesource.com/c/155929
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
@mknyszek mknyszek mentioned this issue Jan 23, 2019
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@sylr sylr mentioned this issue May 15, 2019
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