Use pages_purge to zero blocks in the extent map.

sdlib/d/gc/memmap.d

@@ -69,7 +69,10 @@ void pages_unmap(void* addr, size_t size) {
 }
 
 void pages_purge(void* addr, size_t size) {
-	auto ret = madvise(addr, size, Madv.Free);
+	import core.stdc.stdio;
+	printf("pages_purge(%p, %ld)\n", addr, size);
+
+	auto ret = madvise(addr, size, Madv.DontNeed);
 	assert(ret == 0, "madvise failed!");
 }
 

sdlib/d/gc/rtree.d

@@ -166,13 +166,23 @@ public:
 
 			auto leaves = getLeaves(cache, ptr);
 			if (leaves is null) {
-				import d.gc.util;
 				ptr = nextPtr;
 				continue;
 			}
 
 			auto key1 = subKey(ptr, 1);
 
+			// If we need to clear the whole page, do so via purging.
+			// XXX: We might want to do it for smaller runs, but this is
+			// more complicated as the alternative path requires atomic ops.
+			if (key1 == 0 && stop >= nextPtr) {
+				import d.gc.memmap;
+				pages_purge(cast(void*) leaves.ptr, typeof(*leaves).sizeof);
+
+				ptr = nextPtr;
+				continue;
+			}
+
 			auto subStop = stop < nextPtr ? stop : nextPtr;
 			while (ptr < subStop) {
 				(*leaves)[key1++].store(T(0));