runtime: allow mem profiles with GOGC=off

Fixes #3586.

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/7304098

diff --git a/src/pkg/runtime/mprof.goc b/src/pkg/runtime/mprof.goc
index 0a821cc241929cf8ff81fe141f444214d9830400..a99afe8bb4f1672a554f485ed836929120a7432f 100644 (file)
--- a/src/pkg/runtime/mprof.goc
+++ b/src/pkg/runtime/mprof.goc
@@ -140,13 +140,11 @@ stkbucket(int32 typ, uintptr *stk, int32 nstk, bool alloc)
        return b;
 }
 
-// Record that a gc just happened: all the 'recent' statistics are now real.
-void
-runtime·MProf_GC(void)
+static void
+MProf_GC(void)
 {
        Bucket *b;
-       
-       runtime·lock(&proflock);
+
        for(b=mbuckets; b; b=b->allnext) {
                b->allocs += b->recent_allocs;
                b->frees += b->recent_frees;
@@ -157,6 +155,14 @@ runtime·MProf_GC(void)
                b->recent_alloc_bytes = 0;
                b->recent_free_bytes = 0;
        }
+}
+
+// Record that a gc just happened: all the 'recent' statistics are now real.
+void
+runtime·MProf_GC(void)
+{
+       runtime·lock(&proflock);
+       MProf_GC();
        runtime·unlock(&proflock);
 }
 
@@ -370,12 +376,28 @@ record(Record *r, Bucket *b)
 func MemProfile(p Slice, include_inuse_zero bool) (n int, ok bool) {
        Bucket *b;
        Record *r;
+       bool clear;
 
        runtime·lock(&proflock);
        n = 0;
-       for(b=mbuckets; b; b=b->allnext)
+       clear = true;
+       for(b=mbuckets; b; b=b->allnext) {
                if(include_inuse_zero || b->alloc_bytes != b->free_bytes)
                        n++;
+               if(b->allocs != 0 || b->frees != 0)
+                       clear = false;
+       }
+       if(clear) {
+               // Absolutely no data, suggesting that a garbage collection
+               // has not yet happened. In order to allow profiling when
+               // garbage collection is disabled from the beginning of execution,
+               // accumulate stats as if a GC just happened, and recount buckets.
+               MProf_GC();
+               n = 0;
+               for(b=mbuckets; b; b=b->allnext)
+                       if(include_inuse_zero || b->alloc_bytes != b->free_bytes)
+                               n++;
+       }
        ok = false;
        if(n <= p.len) {
                ok = true;