Align pagemap entries to OS_PAGE_SIZE

Guarantee the page map is page aligned.  Fix public API.

src/mem/largealloc.h

@@ -51,6 +51,13 @@ namespace snmalloc
       return std::make_pair(r, size);
     }
 
+    void new_block()
+    {
+      auto r_size = reserve_block();
+      bump = (size_t)r_size.first;
+      remaining = r_size.second;
+    }
+
   public:
     /**
      * Stack of large allocations that have been returned for reuse.
@@ -61,7 +68,7 @@ namespace snmalloc
      * Primitive allocator for structure that are required before
      * the allocator can be running.
      ***/
-    void* alloc_chunk(size_t size)
+    void* alloc_chunk(size_t size, size_t alignment = 64)
     {
       // Cache line align
       size = bits::align_up(size, 64);
@@ -70,12 +77,20 @@ namespace snmalloc
       {
         FlagLock f(lock);
 
+        auto aligned_bump = bits::align_up(bump, alignment);
+        if ((aligned_bump - bump) < size)
+        {
+          new_block();
+        }
+        else
+        {
+          remaining -= aligned_bump - bump;
+          bump = aligned_bump;
+        }
+
         if (remaining < size)
         {
-          auto r_size = reserve_block();
-
-          bump = (size_t)r_size.first;
-          remaining = r_size.second;
+          new_block();
         }
 
         p = (void*)bump;

src/mem/pagemap.h

@@ -86,7 +86,8 @@ namespace snmalloc
                 value, (PagemapEntry*)LOCKED_ENTRY, std::memory_order_relaxed))
           {
             auto& v = default_memory_provider;
-            value = (PagemapEntry*)v.alloc_chunk(PAGEMAP_NODE_SIZE);
+            value =
+              (PagemapEntry*)v.alloc_chunk(PAGEMAP_NODE_SIZE, OS_PAGE_SIZE);
             e->store(value, std::memory_order_release);
           }
           else
@@ -160,6 +161,13 @@ namespace snmalloc
       return &(leaf_ix.first->values[leaf_ix.second]);
     }
 
+    std::atomic<T>* get_ptr(void* p)
+    {
+      bool success;
+      return get_addr<true>(p, success);
+    }
+
+  public:
     /**
      * Returns the index of a pagemap entry within a given page.  This is used
      * in code that propagates changes to the pagemap elsewhere.
@@ -182,13 +190,6 @@ namespace snmalloc
         reinterpret_cast<uintptr_t>(get_addr<true>(p, success)));
     }
 
-    std::atomic<T>* get_ptr(void* p)
-    {
-      bool success;
-      return get_addr<true>(p, success);
-    }
-
-  public:
     T get(void* p)
     {
       bool success;