Configurable client meta-data

src/snmalloc/backend/fixedglobalconfig.h

@@ -15,6 +15,7 @@ namespace snmalloc
   {
   public:
     using PagemapEntry = DefaultPagemapEntry<ClientMetaDataProvider>;
+    using ClientMeta = ClientMetaDataProvider;
 
   private:
     using ConcretePagemap =

src/snmalloc/backend/globalconfig.h

@@ -32,6 +32,7 @@ namespace snmalloc
   public:
     using Pal = DefaultPal;
     using PagemapEntry = DefaultPagemapEntry<ClientMetaDataProvider>;
+    using ClientMeta = ClientMetaDataProvider;
 
   private:
     using ConcretePagemap =

src/snmalloc/backend_helpers/commonconfig.h

@@ -98,12 +98,14 @@ namespace snmalloc
   struct NoClientMetaDataProvider
   {
     using StorageType = Empty;
+    using DataRef = Empty&;
+    using ConstDataRef = const Empty&;
 
     static size_t required_count(size_t) {
       return 1;
     }
 
-    static Empty& get(Empty* base, size_t) {
+    static DataRef get(StorageType* base, size_t) {
       return *base;
     }
   };
@@ -112,12 +114,14 @@ namespace snmalloc
   struct ArrayClientMetaDataProvider
   {
     using StorageType = T;
+    using DataRef = T&;
+    using ConstDataRef = const T&;
 
     static size_t required_count(size_t max_count) {
       return max_count;
     }
 
-    static T& get(StorageType* base, size_t index) {
+    static DataRef get(StorageType* base, size_t index) {
       return base[index];
     }
   };

src/snmalloc/global/libc.h

@@ -176,4 +176,17 @@ namespace snmalloc::libc
     *memptr = p;
     return 0;
   }
+
+  inline typename snmalloc::Alloc::Config::ClientMeta::DataRef
+  get_client_meta_data(void* p)
+  {
+    return ThreadAlloc::get().get_client_meta_data(p);
+  }
+
+  inline typename snmalloc::Alloc::Config::ClientMeta::ConstDataRef
+  get_client_meta_data_const(void* p)
+  {
+    return ThreadAlloc::get().get_client_meta_data_const(p);
+  }
+
 } // namespace snmalloc::libc

src/snmalloc/mem/corealloc.h

@@ -798,7 +798,6 @@ namespace snmalloc
 
       // Calculate the extra bytes required to store the client meta-data.
       size_t extra_bytes = BackendSlabMetadata::get_extra_bytes(sizeclass);
-      message<1024>("extra_bytes={}, sizeclass={}", extra_bytes, sizeclass);
 
       auto [slab, meta] = Config::Backend::alloc_chunk(
         get_backend_local_state(),

src/snmalloc/mem/localalloc.h

@@ -816,6 +816,49 @@ namespace snmalloc
       }
     }
 
+    /**
+     * @brief Get the client meta data for the snmalloc allocation covering this pointer.
+     * 
+     */
+    typename Config::ClientMeta::DataRef get_client_meta_data(void* p)
+    {
+      const PagemapEntry& entry = Config::Backend::template get_metaentry(address_cast(p));
+
+      size_t index = slab_index(entry.get_sizeclass(), address_cast(p));
+
+      auto* meta_slab = entry.get_slab_metadata();
+
+      if (SNMALLOC_UNLIKELY(meta_slab == nullptr))
+      {
+        // TODO handle const case, where we read fake meta-data.
+        abort();
+      }
+
+      return meta_slab->get_meta_for_object(index);
+    }
+
+    /**
+     * @brief Get the client meta data for the snmalloc allocation covering this pointer.
+     * 
+     */
+    typename Config::ClientMeta::ConstDataRef get_client_meta_data_const(void* p)
+    {
+      const PagemapEntry& entry = Config::Backend::template get_metaentry(address_cast(p));
+
+      size_t index = slab_index(entry.get_sizeclass(), address_cast(p));
+
+      auto* meta_slab = entry.get_slab_metadata();
+
+      if (SNMALLOC_UNLIKELY(meta_slab == nullptr))
+      {
+        static typename Config::ClientMeta::StorageType null_meta_store{};
+        return Config::ClientMeta::get(&null_meta_store, 0);
+      }
+
+      return meta_slab->get_meta_for_object(index);
+    }
+
+
     /**
      * Returns the number of remaining bytes in an object.
      *

src/snmalloc/mem/metadata.h

@@ -372,7 +372,7 @@ namespace snmalloc
     friend class FrontendSlabMetadata;
 
     // Can only be constructed by FrontendSlabMetadata
-    FrontendSlabMetadata_Trait() = default;
+    constexpr FrontendSlabMetadata_Trait() = default;
   };
 
   /**
@@ -434,7 +434,7 @@ namespace snmalloc
      * slab. The meta data will actually allocate multiple elements after this
      * type, so that client_meta_[1] will work for the required meta-data size.
      */
-    SNMALLOC_NO_UNIQUE_ADDRESS typename ClientMeta::StorageType client_meta_;
+    SNMALLOC_NO_UNIQUE_ADDRESS typename ClientMeta::StorageType client_meta_{};
 
     uint16_t& needed()
     {
@@ -601,9 +601,9 @@ namespace snmalloc
       return address_cast(free_queue.read_head(0, key));
     }
 
-    typename ClientMeta::StorageType* get_client_meta_base()
+    typename ClientMeta::DataRef get_meta_for_object(size_t index)
     {
-      return &client_meta_;
+      return ClientMeta::get(&client_meta_, index);
     }
 
     static size_t get_client_storage_count(smallsizeclass_t sizeclass)

src/snmalloc/mem/sizeclasstable.h

@@ -333,14 +333,11 @@ namespace snmalloc
       .capacity;
   }
 
-  constexpr address_t start_of_object(sizeclass_t sc, address_t addr)
+  SNMALLOC_FAST_PATH constexpr size_t slab_index(sizeclass_t sc, address_t addr)
   {
     auto meta = sizeclass_metadata.fast(sc);
-    address_t slab_start = addr & ~meta.slab_mask;
     size_t offset = addr & meta.slab_mask;
-    size_t size = meta.size;
-
-    if constexpr (sizeof(addr) >= 8)
+    if constexpr (sizeof(offset) >= 8)
     {
       // Only works for 64 bit multiplication, as the following will overflow in
       // 32bit.
@@ -351,17 +348,26 @@ namespace snmalloc
       // the slab_mask by making the `div_mult` zero. The link uses 128 bit
       // multiplication, we have shrunk the range of the calculation to remove
       // this dependency.
-      size_t offset_start = ((offset * meta.div_mult) >> DIV_MULT_SHIFT) * size;
-      return slab_start + offset_start;
+      size_t index = ((offset * meta.div_mult) >> DIV_MULT_SHIFT);
+      return index;
     }
     else
     {
+      size_t size = meta.size;
       if (size == 0)
         return 0;
-      return slab_start + (offset / size) * size;
+      return offset / size;
     }
   }
 
+  SNMALLOC_FAST_PATH constexpr address_t start_of_object(sizeclass_t sc, address_t addr)
+  {
+    auto meta = sizeclass_metadata.fast(sc);
+    address_t slab_start = addr & ~meta.slab_mask;
+    size_t index = slab_index(sc, addr);
+    return slab_start + (index * meta.size);
+  }
+
   constexpr size_t index_in_object(sizeclass_t sc, address_t addr)
   {
     return addr - start_of_object(sc, addr);

src/snmalloc/pal/pal_posix.h

@@ -9,7 +9,6 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
-#include <stdlib.h>
 #include <string.h>
 #include <strings.h>
 #include <sys/mman.h>

src/test/func/domestication/domestication.cc

@@ -24,6 +24,7 @@ namespace snmalloc
   public:
     using Pal = DefaultPal;
     using PagemapEntry = DefaultPagemapEntry<NoClientMetaDataProvider>;
+    using ClientMeta = NoClientMetaDataProvider;
 
   private:
     using ConcretePagemap =