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doc/go1.19: add release notes for the soft memory limit and idle GC

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This change resolves some TODOs in the release notes, and while we're
here, also clarifies how CPU profile samples are represented in runtime
traces.

Change-Id: Idaa36ccf65b03fd5463b2d5da682d3fa578d2f46
Reviewed-on: https://go-review.googlesource.com/c/go/+/410356
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Michael Anthony Knyszek 2022-06-04 05:42:30 +00:00 committed by Michael Pratt
parent a71ca3dfbd
commit acfff42802
1 changed files with 29 additions and 4 deletions
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doc/go1.19.html
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@ -82,12 +82,37 @@ Do not send CLs removing the interior tags from such phrases.
<h2 id="runtime">Runtime</h2> <h2 id="runtime">Runtime</h2>
<p><!-- https://go.dev/issue/48409 --> <p><!-- https://go.dev/issue/48409 --><!-- CL 397018 -->
TODO: soft memory limit The runtime now includes support for a soft memory limit. This memory limit
includes all memory mapped and managed by the runtime, and excludes external
memory sources such as binary size, memory managed in other languages, and
memory held by the operating system on behalf of the Go program. This limit
may be managed via the <code>GOMEMLIMIT</code> environment variable or the
<code>SetMemoryLimit</code> function in the runtime/debug package. The limit
works in conjunction with <code>GOGC</code> and <code>SetGCPercent</code>,
and will be respected even if <code>GOGC=off</code>, allowing Go programs to
always make maximal use of their memory limit, improving resource efficiency
in some cases. Please note that small memory limits, on the order of tens of
megabytes or less, are less likely to be adhered to due to external latency
factors, such as OS scheduling. See https://go.dev/issue/52433 for more
details. Larger memory limits, on the order of hundreds of megabytes or more,
are stable and production-ready.
</p>
<p><!-- CL 353989 -->
In order to limit the effects of GC thrashing when the program's live heap
size approaches the soft memory limit, the Go runtime also attempts to limit
total GC CPU utilization to 50%, excluding idle time, choosing to use more
memory over preventing application progress. In practice, we expect this limit
to only play a role in exceptional cases, and the new runtime/metrics metric
<code>/gc/limiter/last-enabled:gc-cycle</code> reports when this last
occurred.
</p> </p>
<p><!-- https://go.dev/issue/44163 --> <p><!-- https://go.dev/issue/44163 -->
TODO: idle mark workers The runtime now schedules many fewer GC worker goroutines on idle operating
system threads when the application is idle enough to force a periodic GC
cycle.
</p> </p>
<p><!-- https://go.dev/issue/18138 --><!-- CL 345889 --> <p><!-- https://go.dev/issue/18138 --><!-- CL 345889 -->
@ -494,7 +519,7 @@ Do not send CLs removing the interior tags from such phrases.
<p><!-- CL 400795 --> <p><!-- CL 400795 -->
When used together with the When used together with the
<a href="/pkg/runtime/pprof#StartCPUProfile">CPU profiler</a>, the <a href="/pkg/runtime/pprof#StartCPUProfile">CPU profiler</a>, the
execution trace includes CPU profile samples. execution trace includes CPU profile samples as instantaneous events.
</p> </p>
</dd> </dd>
</dl><!-- runtime/trace --> </dl><!-- runtime/trace -->