runtime: fix span unusedsince setup

Update #8832

This is probably not the root cause of the issue.
Resolve TODO about setting unusedsince on a wrong span.

Change-Id: I69c87e3d93cb025e3e6fa80a8cffba6ad6ad1395
Reviewed-on: https://go-review.googlesource.com/4390
Reviewed-by: Keith Randall <khr@golang.org>

diff --git a/src/runtime/mheap.go b/src/runtime/mheap.go
index 11bc809ec1d036a12957c8494f98afb6855ad99e..13f1b363d0b83d985ab8913ce2596a32dc6a15c7 100644 (file)
--- a/src/runtime/mheap.go
+++ b/src/runtime/mheap.go
@@ -318,8 +318,7 @@ HaveSpan:
                t.needzero = s.needzero
                s.state = _MSpanStack // prevent coalescing with s
                t.state = _MSpanStack
-               mHeap_FreeSpanLocked(h, t, false, false)
-               t.unusedsince = s.unusedsince // preserve age (TODO: wrong: t is possibly merged and/or deallocated at this point)
+               mHeap_FreeSpanLocked(h, t, false, false, s.unusedsince)
                s.state = _MSpanFree
        }
        s.unusedsince = 0
@@ -395,7 +394,7 @@ func mHeap_Grow(h *mheap, npage uintptr) bool {
        h_spans[p+s.npages-1] = s
        atomicstore(&s.sweepgen, h.sweepgen)
        s.state = _MSpanInUse
-       mHeap_FreeSpanLocked(h, s, false, true)
+       mHeap_FreeSpanLocked(h, s, false, true, 0)
        return true
 }
 
@@ -442,7 +441,7 @@ func mHeap_Free(h *mheap, s *mspan, acct int32) {
                        memstats.heap_alloc -= uint64(s.npages << _PageShift)
                        memstats.heap_objects--
                }
-               mHeap_FreeSpanLocked(h, s, true, true)
+               mHeap_FreeSpanLocked(h, s, true, true, 0)
                if trace.enabled {
                        traceHeapAlloc()
                }
@@ -458,11 +457,11 @@ func mHeap_FreeStack(h *mheap, s *mspan) {
        s.needzero = 1
        lock(&h.lock)
        memstats.stacks_inuse -= uint64(s.npages << _PageShift)
-       mHeap_FreeSpanLocked(h, s, true, true)
+       mHeap_FreeSpanLocked(h, s, true, true, 0)
        unlock(&h.lock)
 }
 
-func mHeap_FreeSpanLocked(h *mheap, s *mspan, acctinuse, acctidle bool) {
+func mHeap_FreeSpanLocked(h *mheap, s *mspan, acctinuse, acctidle bool, unusedsince int64) {
        switch s.state {
        case _MSpanStack:
                if s.ref != 0 {
@@ -488,7 +487,10 @@ func mHeap_FreeSpanLocked(h *mheap, s *mspan, acctinuse, acctidle bool) {
 
        // Stamp newly unused spans. The scavenger will use that
        // info to potentially give back some pages to the OS.
-       s.unusedsince = nanotime()
+       s.unusedsince = unusedsince
+       if unusedsince == 0 {
+               s.unusedsince = nanotime()
+       }
        s.npreleased = 0
 
        // Coalesce with earlier, later spans.