Modify the binder to request 1M - 2 pages instead of 1M. The backing store

in the kernel requires a guard page, so 1M allocations fragment memory very
badly.  Subtracting a couple of pages so that they fit in a power of
two allows the kernel to make more efficient use of its virtual address space.

Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>

libs/binder/ProcessState.cpp

@@ -41,7 +41,7 @@
 #include <sys/mman.h>
 #include <sys/stat.h>
 
-#define BINDER_VM_SIZE (1*1024*1024)
+#define BINDER_VM_SIZE ((1*1024*1024) - (4096 *2))
 
 static bool gSingleProcess = false;