05e6d28849
In Go 1.12, we changed the runtime to use MADV_FREE when available on Linux (falling back to MADV_DONTNEED) in CL 135395 to address issue #23687. While MADV_FREE is somewhat faster than MADV_DONTNEED, it doesn't affect many of the statistics that MADV_DONTNEED does until the memory is actually reclaimed under OS memory pressure. This generally leads to poor user experience, like confusing stats in top and other monitoring tools; and bad integration with management systems that respond to memory usage. We've seen numerous issues about this user experience, including #41818, #39295, #37585, #33376, and #30904, many questions on Go mailing lists, and requests for mechanisms to change this behavior at run-time, such as #40870. There are also issues that may be a result of this, but root-causing it can be difficult, such as #41444 and #39174. And there's some evidence it may even be incompatible with Android's process management in #37569. This CL changes the default to prefer MADV_DONTNEED over MADV_FREE, to favor user-friendliness and minimal surprise over performance. I think it's become clear that Linux's implementation of MADV_FREE ultimately doesn't meet our needs. We've also made many improvements to the scavenger since Go 1.12. In particular, it is now far more prompt and it is self-paced, so it will simply trickle memory back to the system a little more slowly with this change. This can still be overridden by setting GODEBUG=madvdontneed=0. Fixes #42330 (meta-issue). Fixes #41818, #39295, #37585, #33376, #30904 (many of which were already closed as "working as intended"). Change-Id: Ib6aa7f2dc8419b32516cc5a5fc402faf576c92e4 Reviewed-on: https://go-review.googlesource.com/c/go/+/267100 Trust: Austin Clements <austin@google.com> Reviewed-by: Michael Knyszek <mknyszek@google.com> |
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