diff options
Diffstat (limited to 'src/runtime/debug')
| -rw-r--r-- | src/runtime/debug/garbage_test.go | 65 |
1 files changed, 55 insertions, 10 deletions
diff --git a/src/runtime/debug/garbage_test.go b/src/runtime/debug/garbage_test.go index 69e769ecf2..c3501408dd 100644 --- a/src/runtime/debug/garbage_test.go +++ b/src/runtime/debug/garbage_test.go @@ -6,6 +6,7 @@ package debug_test import ( "internal/testenv" + "os" "runtime" . "runtime/debug" "testing" @@ -87,21 +88,65 @@ func TestReadGCStats(t *testing.T) { } } -var big = make([]byte, 1<<20) +var big []byte func TestFreeOSMemory(t *testing.T) { - var ms1, ms2 runtime.MemStats + // Tests FreeOSMemory by making big susceptible to collection + // and checking that at least that much memory is returned to + // the OS after. - if big == nil { - t.Skip("test is not reliable when run multiple times") - } - big = nil + const bigBytes = 32 << 20 + big = make([]byte, bigBytes) + + // Make sure any in-progress GCs are complete. runtime.GC() - runtime.ReadMemStats(&ms1) + + var before runtime.MemStats + runtime.ReadMemStats(&before) + + // Clear the last reference to the big allocation, making it + // susceptible to collection. + big = nil + + // FreeOSMemory runs a GC cycle before releasing memory, + // so it's fine to skip a GC here. + // + // It's possible the background scavenger runs concurrently + // with this function and does most of the work for it. + // If that happens, it's OK. What we want is a test that fails + // often if FreeOSMemory does not work correctly, and a test + // that passes every time if it does. FreeOSMemory() - runtime.ReadMemStats(&ms2) - if ms1.HeapReleased >= ms2.HeapReleased { - t.Errorf("released before=%d; released after=%d; did not go up", ms1.HeapReleased, ms2.HeapReleased) + + var after runtime.MemStats + runtime.ReadMemStats(&after) + + // Check to make sure that the big allocation (now freed) + // had its memory shift into HeapReleased as a result of that + // FreeOSMemory. + if after.HeapReleased <= before.HeapReleased { + t.Fatalf("no memory released: %d -> %d", before.HeapReleased, after.HeapReleased) + } + + // Check to make sure bigBytes was released, plus some slack. Pages may get + // allocated in between the two measurements above for a variety for reasons, + // most commonly for GC work bufs. Since this can get fairly high, depending + // on scheduling and what GOMAXPROCS is, give a lot of slack up-front. + // + // Add a little more slack too if the page size is bigger than the runtime page size. + // "big" could end up unaligned on its ends, forcing the scavenger to skip at worst + // 2x pages. + slack := uint64(bigBytes / 2) + pageSize := uint64(os.Getpagesize()) + if pageSize > 8<<10 { + slack += pageSize * 2 + } + if slack > bigBytes { + // We basically already checked this. + return + } + if after.HeapReleased-before.HeapReleased < bigBytes-slack { + t.Fatalf("less than %d released: %d -> %d", bigBytes, before.HeapReleased, after.HeapReleased) } } |