New configuration of slab sizes for OE.

src/mem/allocconfig.h

@@ -50,6 +50,15 @@ namespace snmalloc
 #endif
     ;
 
+  // Specifies even smaller slab and super slab sizes for open enclave.
+  static constexpr size_t REALLY_ADDRESS_SPACE_CONSTRAINED =
+#ifdef IS_REALLY_ADDRESS_SPACE_CONSTRAINED
+    true
+#else
+    false
+#endif
+    ;
+
   static constexpr size_t RESERVE_MULTIPLE =
 #ifdef USE_RESERVE_MULTIPLE
     USE_RESERVE_MULTIPLE
@@ -100,14 +109,17 @@ namespace snmalloc
   static constexpr size_t MIN_ALLOC_BITS = bits::ctz_const(MIN_ALLOC_SIZE);
 
   // Slabs are 64 KiB unless constrained to 16 KiB.
-  static constexpr size_t SLAB_BITS = ADDRESS_SPACE_CONSTRAINED ? 14 : 16;
+  static constexpr size_t SLAB_BITS = REALLY_ADDRESS_SPACE_CONSTRAINED ?
+    13 :
+    (ADDRESS_SPACE_CONSTRAINED ? 14 : 16);
   static constexpr size_t SLAB_SIZE = 1 << SLAB_BITS;
   static constexpr size_t SLAB_MASK = ~(SLAB_SIZE - 1);
 
   // Superslabs are composed of this many slabs. Slab offsets are encoded as
   // a byte, so the maximum count is 256. This must be a power of two to
   // allow fast masking to find a superslab start address.
-  static constexpr size_t SLAB_COUNT_BITS = ADDRESS_SPACE_CONSTRAINED ? 6 : 8;
+  static constexpr size_t SLAB_COUNT_BITS =
+    REALLY_ADDRESS_SPACE_CONSTRAINED ? 5 : (ADDRESS_SPACE_CONSTRAINED ? 6 : 8);
   static constexpr size_t SLAB_COUNT = 1 << SLAB_COUNT_BITS;
   static constexpr size_t SUPERSLAB_SIZE = SLAB_SIZE * SLAB_COUNT;
   static constexpr size_t SUPERSLAB_MASK = ~(SUPERSLAB_SIZE - 1);

src/test/func/two_alloc_types/alloc2.cc

@@ -1,4 +1,7 @@
-#undef IS_ADDRESS_SPACE_CONSTRAINED
+// Remove parameters feed from test harness
+#undef ADDRESS_SPACE_CONSTRAINED
+#undef REALLY_ADDRESS_SPACE_CONSTRAINED
+
 #define SNMALLOC_NAME_MANGLE(a) host_##a
 #define NO_BOOTSTRAP_ALLOCATOR
 #define SNMALLOC_EXPOSE_PAGEMAP