From c5dea8f38726572ddc161e5d169a453639edb7b1 Mon Sep 17 00:00:00 2001 From: Michael Anthony Knyszek Date: Mon, 3 Aug 2020 19:27:59 +0000 Subject: [PATCH] runtime: remove memstats.heap_idle This statistic is updated in many places but for MemStats may be computed from existing statistics. Specifically by definition heap_idle = heap_sys - heap_inuse since heap_sys is all memory allocated from the OS for use in the heap minus memory used for non-heap purposes. heap_idle is almost the same (since it explicitly includes memory that *could* be used for non-heap purposes) but also doesn't include memory that's actually used to hold heap objects. Although it has some utility as a sanity check, it complicates accounting and we want fewer, orthogonal statistics for upcoming metrics changes, so just drop it. Change-Id: I40af54a38e335f43249f6e218f35088bfd4380d1 Reviewed-on: https://go-review.googlesource.com/c/go/+/246974 Run-TryBot: Michael Knyszek TryBot-Result: Go Bot Trust: Michael Knyszek Reviewed-by: Michael Pratt --- src/runtime/heapdump.go | 2 +- src/runtime/mheap.go | 3 --- src/runtime/mstats.go | 19 +++++++++++++++++-- 3 files changed, 18 insertions(+), 6 deletions(-) diff --git a/src/runtime/heapdump.go b/src/runtime/heapdump.go index eed47930f0..f96475e848 100644 --- a/src/runtime/heapdump.go +++ b/src/runtime/heapdump.go @@ -552,7 +552,7 @@ func dumpmemstats() { dumpint(memstats.nfree) dumpint(memstats.heap_alloc) dumpint(memstats.heap_sys.load()) - dumpint(memstats.heap_idle) + dumpint(memstats.heap_sys.load() - memstats.heap_inuse) dumpint(memstats.heap_inuse) dumpint(memstats.heap_released) dumpint(memstats.heap_objects) diff --git a/src/runtime/mheap.go b/src/runtime/mheap.go index 1624a04b9d..87d2fd495b 100644 --- a/src/runtime/mheap.go +++ b/src/runtime/mheap.go @@ -1239,7 +1239,6 @@ HaveSpan: // Manually managed memory doesn't count toward heap_sys. memstats.heap_sys.add(-int64(nbytes)) } - atomic.Xadd64(&memstats.heap_idle, -int64(nbytes)) // Publish the span in various locations. @@ -1317,7 +1316,6 @@ func (h *mheap) grow(npage uintptr) bool { // size which is always > physPageSize, so its safe to // just add directly to heap_released. atomic.Xadd64(&memstats.heap_released, int64(asize)) - atomic.Xadd64(&memstats.heap_idle, int64(asize)) // Recalculate nBase. // We know this won't overflow, because sysAlloc returned @@ -1417,7 +1415,6 @@ func (h *mheap) freeSpanLocked(s *mspan, typ spanAllocType) { // Manually managed memory doesn't count toward heap_sys, so add it back. memstats.heap_sys.add(int64(nbytes)) } - atomic.Xadd64(&memstats.heap_idle, int64(nbytes)) // Mark the space as free. h.pages.free(s.base(), s.npages) diff --git a/src/runtime/mstats.go b/src/runtime/mstats.go index 967fe6e2be..43f74273f7 100644 --- a/src/runtime/mstats.go +++ b/src/runtime/mstats.go @@ -34,7 +34,6 @@ type mstats struct { // in manually-managed spans. heap_alloc uint64 // bytes allocated and not yet freed (same as alloc above) heap_sys sysMemStat // virtual address space obtained from system for GC'd heap - heap_idle uint64 // bytes in idle spans heap_inuse uint64 // bytes in mSpanInUse spans heap_released uint64 // bytes released to the os @@ -461,7 +460,23 @@ func readmemstats_m(stats *MemStats) { stats.Frees = memstats.nfree stats.HeapAlloc = memstats.heap_alloc stats.HeapSys = memstats.heap_sys.load() - stats.HeapIdle = memstats.heap_idle + // By definition, HeapIdle is memory that was mapped + // for the heap but is not currently used to hold heap + // objects. It also specifically is memory that can be + // used for other purposes, like stacks, but this memory + // is subtracted out of HeapSys before it makes that + // transition. Put another way: + // + // heap_sys = bytes allocated from the OS for the heap - bytes ultimately used for non-heap purposes + // heap_idle = bytes allocated from the OS for the heap - bytes ultimately used for any purpose + // + // or + // + // heap_sys = sys - stacks_inuse - gcWorkBufInUse - gcProgPtrScalarBitsInUse + // heap_idle = sys - stacks_inuse - gcWorkBufInUse - gcProgPtrScalarBitsInUse - heap_inuse + // + // => heap_idle = heap_sys - heap_inuse + stats.HeapIdle = memstats.heap_sys.load() - memstats.heap_inuse stats.HeapInuse = memstats.heap_inuse stats.HeapReleased = memstats.heap_released stats.HeapObjects = memstats.heap_objects -- 2.48.1