runtime: sample large heap allocations correctly
Remove an unnecessary check on the heap sampling code that forced sampling
of all heap allocations larger than the sampling rate. This need to follow
a poisson process so that they can be correctly unsampled. Maintain a check
for MemProfileRate==1 to provide a mechanism for full sampling, as
documented in https://golang.org/pkg/runtime/#pkg-variables.
Additional testing for this change is on cl/129117.
Fixes #26618
Change-Id: I7802bde2afc655cf42cffac34af9bafeb3361957
GitHub-Last-Rev: 471f747af845395d458096bea26daa93b91120be
GitHub-Pull-Request: golang/go#29791
Reviewed-on: https://go-review.googlesource.com/c/158337
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index c1a89dc..8c617bb 100644
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -1012,7 +1012,7 @@
}
if rate := MemProfileRate; rate > 0 {
- if size < uintptr(rate) && int32(size) < c.next_sample {
+ if rate != 1 && int32(size) < c.next_sample {
c.next_sample -= int32(size)
} else {
mp := acquirem()
diff --git a/src/runtime/testdata/testprog/memprof.go b/src/runtime/testdata/testprog/memprof.go
index a22fee6..7b134bc 100644
--- a/src/runtime/testdata/testprog/memprof.go
+++ b/src/runtime/testdata/testprog/memprof.go
@@ -21,7 +21,10 @@
var memProfStr string
func MemProf() {
- for i := 0; i < 1000; i++ {
+ // Force heap sampling for determinism.
+ runtime.MemProfileRate = 1
+
+ for i := 0; i < 10; i++ {
fmt.Fprintf(&memProfBuf, "%*d\n", i, i)
}
memProfStr = memProfBuf.String()
