runtime: use uintptr instead of int32 for counting to next heap profile sample
Overflow of the comparison caused very large (>=1<<32) allocations to
sometimes not get sampled at all. Use uintptr so the comparison will
never overflow.
Fixes #33342
Tested on the example in 33342. I don't want to check a test in that
needs that much memory, however.
Change-Id: I51fe77a9117affed8094da93c0bc5f445ac2d3d3
Reviewed-on: https://go-review.googlesource.com/c/go/+/188017
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index 8ad7035..5a21e80 100644
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -1075,8 +1075,8 @@
}
if rate := MemProfileRate; rate > 0 {
- if rate != 1 && int32(size) < c.next_sample {
- c.next_sample -= int32(size)
+ if rate != 1 && size < c.next_sample {
+ c.next_sample -= size
} else {
mp := acquirem()
profilealloc(mp, x, size)
@@ -1170,7 +1170,7 @@
// processes, the distance between two samples follows the exponential
// distribution (exp(MemProfileRate)), so the best return value is a random
// number taken from an exponential distribution whose mean is MemProfileRate.
-func nextSample() int32 {
+func nextSample() uintptr {
if GOOS == "plan9" {
// Plan 9 doesn't support floating point in note handler.
if g := getg(); g == g.m.gsignal {
@@ -1178,7 +1178,7 @@
}
}
- return fastexprand(MemProfileRate)
+ return uintptr(fastexprand(MemProfileRate))
}
// fastexprand returns a random number from an exponential distribution with
@@ -1213,14 +1213,14 @@
// nextSampleNoFP is similar to nextSample, but uses older,
// simpler code to avoid floating point.
-func nextSampleNoFP() int32 {
+func nextSampleNoFP() uintptr {
// Set first allocation sample size.
rate := MemProfileRate
if rate > 0x3fffffff { // make 2*rate not overflow
rate = 0x3fffffff
}
if rate != 0 {
- return int32(fastrand() % uint32(2*rate))
+ return uintptr(fastrand() % uint32(2*rate))
}
return 0
}
diff --git a/src/runtime/mcache.go b/src/runtime/mcache.go
index 0cb21f7..d4fa9a0 100644
--- a/src/runtime/mcache.go
+++ b/src/runtime/mcache.go
@@ -19,7 +19,7 @@
type mcache struct {
// The following members are accessed on every malloc,
// so they are grouped here for better caching.
- next_sample int32 // trigger heap sample after allocating this many bytes
+ next_sample uintptr // trigger heap sample after allocating this many bytes
local_scan uintptr // bytes of scannable heap allocated
// Allocator cache for tiny objects w/o pointers.
