From 7c58ef732efd9bf0d0882bb95371ce1909924a75 Mon Sep 17 00:00:00 2001 From: Martin Möhrmann Date: Mon, 14 Sep 2020 16:55:34 +0200 Subject: runtime: implement GODEBUG=inittrace=1 support MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Setting inittrace=1 causes the runtime to emit a single line to standard error for each package with init work, summarizing the execution time and memory allocation. The emitted debug information for init functions can be used to find bottlenecks or regressions in Go startup performance. Packages with no init function work (user defined or compiler generated) are omitted. Tracing plugin inits is not supported as they can execute concurrently. This would make the implementation of tracing more complex while adding support for a very rare use case. Plugin inits can be traced separately by testing a main package importing the plugins package imports explicitly. $ GODEBUG=inittrace=1 go test init internal/bytealg @0.008 ms, 0 ms clock, 0 bytes, 0 allocs init runtime @0.059 ms, 0.026 ms clock, 0 bytes, 0 allocs init math @0.19 ms, 0.001 ms clock, 0 bytes, 0 allocs init errors @0.22 ms, 0.004 ms clock, 0 bytes, 0 allocs init strconv @0.24 ms, 0.002 ms clock, 32 bytes, 2 allocs init sync @0.28 ms, 0.003 ms clock, 16 bytes, 1 allocs init unicode @0.44 ms, 0.11 ms clock, 23328 bytes, 24 allocs ... Inspired by stapelberg@google.com who instrumented doInit in a prototype to measure init times with GDB. Fixes #41378 Change-Id: Ic37c6a0cfc95488de9e737f5e346b8dbb39174e1 Reviewed-on: https://go-review.googlesource.com/c/go/+/254659 Trust: Martin Möhrmann Run-TryBot: Martin Möhrmann TryBot-Result: Go Bot Reviewed-by: Keith Randall --- src/runtime/runtime1.go | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) (limited to 'src/runtime/runtime1.go') diff --git a/src/runtime/runtime1.go b/src/runtime/runtime1.go index 7c893aa25c..0f182ac58e 100644 --- a/src/runtime/runtime1.go +++ b/src/runtime/runtime1.go @@ -300,7 +300,6 @@ type dbgVar struct { // existing int var for that value, which may // already have an initial value. var debug struct { - allocfreetrace int32 cgocheck int32 clobberfree int32 efence int32 @@ -311,13 +310,20 @@ var debug struct { gctrace int32 invalidptr int32 madvdontneed int32 // for Linux; issue 28466 - sbrk int32 scavenge int32 scavtrace int32 scheddetail int32 schedtrace int32 tracebackancestors int32 asyncpreemptoff int32 + + // debug.malloc is used as a combined debug check + // in the malloc function and should be set + // if any of the below debug options is != 0. + malloc bool + allocfreetrace int32 + inittrace int32 + sbrk int32 } var dbgvars = []dbgVar{ @@ -339,6 +345,7 @@ var dbgvars = []dbgVar{ {"schedtrace", &debug.schedtrace}, {"tracebackancestors", &debug.tracebackancestors}, {"asyncpreemptoff", &debug.asyncpreemptoff}, + {"inittrace", &debug.inittrace}, } func parsedebugvars() { @@ -378,6 +385,8 @@ func parsedebugvars() { } } + debug.malloc = (debug.allocfreetrace | debug.inittrace | debug.sbrk) != 0 + setTraceback(gogetenv("GOTRACEBACK")) traceback_env = traceback_cache } -- cgit v1.3 From 05e6d28849293266028c0bc9e9b0f8d0da38a2e2 Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Sun, 1 Nov 2020 17:48:42 -0500 Subject: runtime: default to MADV_DONTNEED on Linux 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 Reviewed-by: Michael Knyszek --- src/runtime/extern.go | 8 ++++---- src/runtime/runtime1.go | 11 +++++++++++ 2 files changed, 15 insertions(+), 4 deletions(-) (limited to 'src/runtime/runtime1.go') diff --git a/src/runtime/extern.go b/src/runtime/extern.go index b75507b8f8..dacdf4f383 100644 --- a/src/runtime/extern.go +++ b/src/runtime/extern.go @@ -91,10 +91,10 @@ It is a comma-separated list of name=val pairs setting these named variables: # bytes memory allocated on the heap # allocs number of heap allocations - madvdontneed: setting madvdontneed=1 will use MADV_DONTNEED - instead of MADV_FREE on Linux when returning memory to the - kernel. This is less efficient, but causes RSS numbers to drop - more quickly. + madvdontneed: setting madvdontneed=0 will use MADV_FREE + instead of MADV_DONTNEED on Linux when returning memory to the + kernel. This is more efficient, but means RSS numbers will + drop only when the OS is under memory pressure. memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate. When set to 0 memory profiling is disabled. Refer to the description of diff --git a/src/runtime/runtime1.go b/src/runtime/runtime1.go index 0f182ac58e..30b7044bff 100644 --- a/src/runtime/runtime1.go +++ b/src/runtime/runtime1.go @@ -352,6 +352,17 @@ func parsedebugvars() { // defaults debug.cgocheck = 1 debug.invalidptr = 1 + if GOOS == "linux" { + // On Linux, MADV_FREE is faster than MADV_DONTNEED, + // but doesn't affect many of the statistics that + // MADV_DONTNEED does until the memory is actually + // reclaimed. 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. + // Hence, default to MADV_DONTNEED. + debug.madvdontneed = 1 + } for p := gogetenv("GODEBUG"); p != ""; { field := "" -- cgit v1.3