runtime/pprof: introduce "allocs" profile

The Go's heap profile contains four kinds of samples
(inuse_space, inuse_objects, alloc_space, and alloc_objects).
The pprof tool by default chooses the inuse_space (the bytes
of live, in-use objects). When analyzing the current memory
usage the choice of inuse_space as the default may be useful,
but in some cases, users are more interested in analyzing the
total allocation statistics throughout the program execution.
For example, when we analyze the memory profile from benchmark
or program test run, we are more likely interested in the whole
allocation history than the live heap snapshot at the end of
the test or benchmark.

The pprof tool provides flags to control which sample type
to be used for analysis. However, it is one of the less-known
features of pprof and we believe it's better to choose the
right type of samples as the default when producing the profile.

This CL introduces a new type of profile, "allocs", which is
the same as the "heap" profile but marks the alloc_space
as the default type unlike heap profiles that use inuse_space
as the default type.

'go test -memprofile=...' command is changed to use the new
"allocs" profile type instead of the traditional "heap" profile.

Fixes #24443

Change-Id: I012dd4b6dcacd45644d7345509936b8380b6fbd9
Reviewed-on: https://go-review.googlesource.com/102696
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Russ Cox <rsc@golang.org>

1 files changed, 4 insertions, 5 deletions

diff --git a/src/cmd/go/internal/test/test.go b/src/cmd/go/internal/test/test.go
index d9931a333e..b95a8c55aa 100644
--- a/src/cmd/go/internal/test/test.go
+++ b/src/cmd/go/internal/test/test.go
@@ -331,14 +331,13 @@ profile the tests during execution:
 	    Writes test binary as -c would.
 
 	-memprofile mem.out
-	    Write a memory profile to the file after all tests have passed.
+	    Write an allocation profile to the file after all tests have passed.
 	    Writes test binary as -c would.
 
 	-memprofilerate n
-	    Enable more precise (and expensive) memory profiles by setting
-	    runtime.MemProfileRate. See 'go doc runtime.MemProfileRate'.
-	    To profile all memory allocations, use -test.memprofilerate=1
-	    and pass --alloc_space flag to the pprof tool.
+	    Enable more precise (and expensive) memory allocation profiles by
+	    setting runtime.MemProfileRate. See 'go doc runtime.MemProfileRate'.
+	    To profile all memory allocations, use -test.memprofilerate=1.
 
 	-mutexprofile mutex.out
 	    Write a mutex contention profile to the specified file