Address space constrained option

CMakeLists.txt

@@ -26,7 +26,13 @@ macro(linklibs project)
 endmacro()
 
 if(MSVC)
-  add_compile_options(/WX /W4 /wd4127 /wd4324 /wd4201 /std:c++latest)
+  # Force to always compile with W4
+  if(CMAKE_CXX_FLAGS MATCHES "/W[0-4]")
+    string(REGEX REPLACE "/W[0-4]" "/W4" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
+  else()
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /W4")
+  endif()
+  add_compile_options(/WX /wd4127 /wd4324 /wd4201)
   set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} /Zi")
   set(CMAKE_EXE_LINKER_FLAGS_RELEASE "${CMAKE_EXE_LINKER_FLAGS_RELEASE} /DEBUG")
 else()

src/ds/aba.h

@@ -97,7 +97,7 @@ namespace snmalloc
         (__int64*)&expect);
 #  else
 #    if defined(__GNUC__) && !defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_16)
-#error You must compile with -mcx16 to enable 16-bit atomic compare and swap.
+#error You must compile with -mcx16 to enable 16-byte atomic compare and swap.
 #    endif
       Cmp xchg{value, expect.aba + 1};
 

src/mem/alloc.h

@@ -140,10 +140,6 @@ namespace snmalloc
     }
   };
 
-  static_assert(
-    SUPERSLAB_SIZE == SuperslabPagemap::GRANULARITY,
-    "The superslab size should be the same as the pagemap granularity");
-
 #ifndef SNMALLOC_DEFAULT_PAGEMAP
 #  define SNMALLOC_DEFAULT_PAGEMAP snmalloc::SuperslabMap
 #endif

src/mem/allocconfig.h

@@ -39,6 +39,17 @@ namespace snmalloc
 #endif
     ;
 
+  // Specifies smaller slab and super slab sizes for address space
+  // constrained scenarios.
+  static constexpr size_t ADDRESS_SPACE_CONSTRAINED =
+#ifdef IS_ADDRESS_SPACE_CONSTRAINED
+    true
+#else
+    // In 32 bit uses smaller superslab.
+    (!bits::is64())
+#endif
+    ;
+
   static constexpr size_t RESERVE_MULTIPLE =
 #ifdef USE_RESERVE_MULTIPLE
     USE_RESERVE_MULTIPLE
@@ -85,14 +96,14 @@ namespace snmalloc
   static constexpr size_t MIN_ALLOC_SIZE = 1 << MIN_ALLOC_BITS;
 
   // Slabs are 64 kb.
-  static constexpr size_t SLAB_BITS = 16;
+  static constexpr size_t SLAB_BITS = 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 = 8;
+  static constexpr size_t SLAB_COUNT_BITS = 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);
@@ -111,8 +122,8 @@ namespace snmalloc
     MIN_ALLOC_SIZE >= (sizeof(void*) * 2),
     "MIN_ALLOC_SIZE must be sufficient for two pointers");
   static_assert(
-    SLAB_BITS == (sizeof(uint16_t) * 8),
-    "SLAB_BITS must be the bits in a uint16_t");
+    SLAB_BITS <= (sizeof(uint16_t) * 8),
+    "SLAB_BITS must not be more than the bits in a uint16_t");
   static_assert(
     SLAB_COUNT == bits::next_pow2_const(SLAB_COUNT),
     "SLAB_COUNT must be a power of 2");

src/mem/pagemap.h

@@ -189,8 +189,6 @@ namespace snmalloc
     }
 
   public:
-    static constexpr size_t GRANULARITY = 1 << GRANULARITY_BITS;
-
     T get(void* p)
     {
       bool success;
@@ -245,10 +243,6 @@ namespace snmalloc
     static constexpr size_t ENTRIES = 1ULL << (COVERED_BITS + CONTENT_BITS);
     static constexpr size_t SHIFT = GRANULARITY_BITS;
 
-  public:
-    static constexpr size_t GRANULARITY = 1 << GRANULARITY_BITS;
-
-  private:
     std::atomic<T> top[ENTRIES];
 
   public:

src/mem/slab.h

@@ -58,7 +58,7 @@ namespace snmalloc
       {
         // This slab is being bump allocated.
         p = (void*)((size_t)this + head - 1);
-        meta->head = head + (uint16_t)rsize;
+        meta->head = (head + (uint16_t)rsize) & (SLAB_SIZE - 1);
         if (meta->head == 1)
         {
           meta->set_full();

src/pal/pal_plain.h

@@ -11,8 +11,6 @@ namespace snmalloc
   class PALPlainMixin : public State
   {
   public:
-    PALPlainMixin() : State() {}
-
     // Notify platform that we will not be using these pages
     void notify_not_using(void*, size_t) noexcept {}