diff --git a/src/pkg/runtime/malloc.goc b/src/pkg/runtime/malloc.goc
index 9e4acc206e..739c61e4f4 100644
--- a/src/pkg/runtime/malloc.goc
+++ b/src/pkg/runtime/malloc.goc
@@ -19,7 +19,6 @@ package runtime
 // Mark mheap as 'no pointers', it does not contain interesting pointers but occupies ~45K.
 #pragma dataflag NOPTR
 MHeap runtime·mheap;
-MStats mstats;
 
 int32	runtime·checking;
 
@@ -321,10 +320,7 @@ runtime·purgecachedstats(MCache *c)
 	}
 }
 
-// Size of the trailing by_size array differs between Go and C,
-// NumSizeClasses was changed, but we can not change Go struct because of backward compatibility.
-// sizeof_C_MStats is what C thinks about size of Go struct.
-uintptr runtime·sizeof_C_MStats = sizeof(MStats) - (NumSizeClasses - 61) * sizeof(mstats.by_size[0]);
+uintptr runtime·sizeof_C_MStats = sizeof(MStats);
 
 #define MaxArena32 (2U<<30)
 
diff --git a/src/pkg/runtime/malloc.h b/src/pkg/runtime/malloc.h
index e07cebc0a0..9f34b55461 100644
--- a/src/pkg/runtime/malloc.h
+++ b/src/pkg/runtime/malloc.h
@@ -90,7 +90,7 @@ typedef struct GCStats	GCStats;
 
 enum
 {
-	PageShift	= 13,
+	PageShift	= 12,
 	PageSize	= 1<<PageShift,
 	PageMask	= PageSize - 1,
 };
@@ -103,7 +103,7 @@ enum
 	// size classes.  NumSizeClasses is that number.  It's needed here
 	// because there are static arrays of this length; when msize runs its
 	// size choosing algorithm it double-checks that NumSizeClasses agrees.
-	NumSizeClasses = 67,
+	NumSizeClasses = 61,
 
 	// Tunable constants.
 	MaxSmallSize = 32<<10,
@@ -255,7 +255,7 @@ struct MStats
 	} by_size[NumSizeClasses];
 };
 
-#define mstats runtime·memStats
+#define mstats runtime·memStats	/* name shared with Go */
 extern MStats mstats;
 
 // Size classes.  Computed and initialized by InitSizes.
diff --git a/src/pkg/runtime/mem.go b/src/pkg/runtime/mem.go
index fa308b5d96..dc735e4a62 100644
--- a/src/pkg/runtime/mem.go
+++ b/src/pkg/runtime/mem.go
@@ -60,8 +60,9 @@ type MemStats struct {
 
 var sizeof_C_MStats uintptr // filled in by malloc.goc
 
+var memStats MemStats
+
 func init() {
-	var memStats MemStats
 	if sizeof_C_MStats != unsafe.Sizeof(memStats) {
 		println(sizeof_C_MStats, unsafe.Sizeof(memStats))
 		panic("MStats vs MemStatsType size mismatch")
diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c
index caab7b9ee6..2c82fb3ac4 100644
--- a/src/pkg/runtime/mgc0.c
+++ b/src/pkg/runtime/mgc0.c
@@ -25,10 +25,6 @@ enum {
 	wordsPerBitmapWord = sizeof(void*)*8/4,
 	bitShift = sizeof(void*)*8/4,
 
-	WorkbufSize	= 16*1024,
-	RootBlockSize	= 4*1024,
-	FinBlockSize	= 4*1024,
-
 	handoffThreshold = 4,
 	IntermediateBufferCapacity = 64,
 
@@ -147,10 +143,11 @@ struct Obj
 	uintptr	ti;	// type info
 };
 
+// The size of Workbuf is N*PageSize.
 typedef struct Workbuf Workbuf;
 struct Workbuf
 {
-#define SIZE (WorkbufSize-sizeof(LFNode)-sizeof(uintptr))
+#define SIZE (2*PageSize-sizeof(LFNode)-sizeof(uintptr))
 	LFNode  node; // must be first
 	uintptr nobj;
 	Obj     obj[SIZE/sizeof(Obj) - 1];
@@ -729,7 +726,7 @@ scanblock(Workbuf *wbuf, bool keepworking)
 	ChanType *chantype;
 	Obj *wp;
 
-	if(sizeof(Workbuf) % WorkbufSize != 0)
+	if(sizeof(Workbuf) % PageSize != 0)
 		runtime·throw("scanblock: size of Workbuf is suboptimal");
 
 	// Memory arena parameters.
@@ -1590,8 +1587,8 @@ runtime·queuefinalizer(byte *p, FuncVal *fn, uintptr nret, Type *fint, PtrType
 	runtime·lock(&finlock);
 	if(finq == nil || finq->cnt == finq->cap) {
 		if(finc == nil) {
-			finc = runtime·persistentalloc(FinBlockSize, 0, &mstats.gc_sys);
-			finc->cap = (FinBlockSize - sizeof(FinBlock)) / sizeof(Finalizer) + 1;
+			finc = runtime·persistentalloc(PageSize, 0, &mstats.gc_sys);
+			finc->cap = (PageSize - sizeof(FinBlock)) / sizeof(Finalizer) + 1;
 			finc->alllink = allfin;
 			allfin = finc;
 		}
@@ -2218,8 +2215,6 @@ gc(struct gc_args *args)
 	runtime·MProf_GC();
 }
 
-extern uintptr runtime·sizeof_C_MStats;
-
 void
 runtime·ReadMemStats(MStats *stats)
 {
@@ -2231,9 +2226,7 @@ runtime·ReadMemStats(MStats *stats)
 	m->gcing = 1;
 	runtime·stoptheworld();
 	updatememstats(nil);
-	// Size of the trailing by_size array differs between Go and C,
-	// NumSizeClasses was changed, but we can not change Go struct because of backward compatibility.
-	runtime·memcopy(runtime·sizeof_C_MStats, stats, &mstats);
+	*stats = mstats;
 	m->gcing = 0;
 	m->locks++;
 	runtime·semrelease(&runtime·worldsema);
diff --git a/src/pkg/runtime/netpoll.goc b/src/pkg/runtime/netpoll.goc
index 81471dca5b..2830f882d8 100644
--- a/src/pkg/runtime/netpoll.goc
+++ b/src/pkg/runtime/netpoll.goc
@@ -34,11 +34,6 @@ package net
 #define READY ((G*)1)
 #define WAIT  ((G*)2)
 
-enum
-{
-	PollBlockSize	= 4*1024,
-};
-
 struct PollDesc
 {
 	PollDesc* link;	// in pollcache, protected by pollcache.Lock
@@ -427,7 +422,7 @@ allocPollDesc(void)
 
 	runtime·lock(&pollcache);
 	if(pollcache.first == nil) {
-		n = PollBlockSize/sizeof(*pd);
+		n = PageSize/sizeof(*pd);
 		if(n == 0)
 			n = 1;
 		// Must be in non-GC memory because can be referenced