runtime: drive proportional sweep directly off heap_live

Currently, proportional sweep maintains its own count of how many
bytes have been allocated since the beginning of the sweep cycle so it
can compute how many pages need to be swept for a given allocation.

However, this requires a somewhat complex reimbursement scheme since
proportional sweep must be done before a span is allocated, but we
don't know how many bytes to charge until we've allocated a span. This
means that the allocated byte count used by proportional sweep can go
up and down, which has led to underflow bugs in the past (#18043) and
is going to interfere with adjusting sweep pacing on-the-fly (for #19076).

This approach also means we're maintaining a statistic that is very
closely related to heap_live, but has a different 0 value. This is
particularly confusing because the sweep ratio is computed based on
heap_live, so you have to understand that these two statistics are
very closely related.

Replace all of this and compute the sweep debt directly from the
current value of heap_live. To make this work, we simply save the
value of heap_live when the sweep ratio is computed to use as a
"basis" for later computing the sweep debt.

This eliminates the need for reimbursement as well as the code for
maintaining the sweeper's version of the live heap size.

For #19076.

Coincidentally fixes #18043, since this eliminates sweep reimbursement
entirely.

Change-Id: I1f931ddd6e90c901a3972c7506874c899251dc2a
Reviewed-on: https://go-review.googlesource.com/39832
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>
4 files changed
tree: a71f8db01608d68a32abaf14a26581fae5634234
  1. .gitattributes
  2. .github/
  3. .gitignore
  4. AUTHORS
  5. CONTRIBUTING.md
  6. CONTRIBUTORS
  7. LICENSE
  8. PATENTS
  9. README.md
  10. api/
  11. doc/
  12. favicon.ico
  13. lib/
  14. misc/
  15. robots.txt
  16. src/
  17. test/
README.md

The Go Programming Language

Go is an open source programming language that makes it easy to build simple, reliable, and efficient software.

Gopher image Gopher image by Renee French, licensed under Creative Commons 3.0 Attributions license.

Our canonical Git repository is located at https://go.googlesource.com/go. There is a mirror of the repository at https://github.com/golang/go.

Unless otherwise noted, the Go source files are distributed under the BSD-style license found in the LICENSE file.

Download and Install

Binary Distributions

Official binary distributions are available at https://golang.org/dl/.

After downloading a binary release, visit https://golang.org/doc/install or load doc/install.html in your web browser for installation instructions.

Install From Source

If a binary distribution is not available for your combination of operating system and architecture, visit https://golang.org/doc/install/source or load doc/install-source.html in your web browser for source installation instructions.

Contributing

Go is the work of hundreds of contributors. We appreciate your help!

To contribute, please read the contribution guidelines: https://golang.org/doc/contribute.html

Note that the Go project does not use GitHub pull requests, and that we use the issue tracker for bug reports and proposals only. See https://golang.org/wiki/Questions for a list of places to ask questions about the Go language.