runtime: switch to new page allocator

This change flips the oldPageAllocator constant enabling the new page
allocator in the Go runtime.

Updates #35112.

Change-Id: I7fc8332af9fd0e43ce28dd5ebc1c1ce519ce6d0c
Reviewed-on: https://go-review.googlesource.com/c/go/+/201765
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

src/runtime/malloc.go

@@ -19,7 +19,7 @@
 //	fixalloc: a free-list allocator for fixed-size off-heap objects,
 //		used to manage storage used by the allocator.
 //	mheap: the malloc heap, managed at page (8192-byte) granularity.
-//	mspan: a run of pages managed by the mheap.
+//	mspan: a run of in-use pages managed by the mheap.
 //	mcentral: collects all spans of a given size class.
 //	mcache: a per-P cache of mspans with free space.
 //	mstats: allocation statistics.
@@ -56,13 +56,8 @@
 //	   it is placed on the mcentral free list for the mspan's size
 //	   class.
 //
-//	3. Otherwise, if all objects in the mspan are free, the mspan
-//	   is now "idle", so it is returned to the mheap and no longer
-//	   has a size class.
-//	   This may coalesce it with adjacent idle mspans.
-//
-//	4. If an mspan remains idle for long enough, return its pages
-//	   to the operating system.
+//	3. Otherwise, if all objects in the mspan are free, the mspan's
+//	   pages are returned to the mheap and the mspan is now dead.
 //
 // Allocating and freeing a large object uses the mheap
 // directly, bypassing the mcache and mcentral.
@@ -324,7 +319,7 @@ const (
 	minLegalPointer uintptr = 4096
 
 	// Whether to use the old page allocator or not.
-	oldPageAllocator = true
+	oldPageAllocator = false
 )
 
 // physPageSize is the size in bytes of the OS's physical pages.