Optimize foliage rendering with concurrent arena allocator

Source/Engine/Core/Memory/Allocation.cpp

@@ -52,3 +52,81 @@ void* ArenaAllocator::Allocate(uint64 size, uint64 alignment)
 
     return mem;
 }
+
+void ConcurrentArenaAllocator::Free()
+{
+    _locker.Lock();
+
+    // Free all pages
+    Page* page = (Page*)_first;
+    while (page)
+    {
+#if COMPILE_WITH_PROFILER
+        ProfilerMemory::OnGroupUpdate(ProfilerMemory::Groups::MallocArena, -(int64)page->Size, -1);
+#endif
+        if (_free1)
+            _free1(page->Memory);
+        else
+            _free2(page->Memory, page->Size);
+        Page* next = page->Next;
+        if (_free1)
+            _free1(page);
+        else
+            _free2(page, sizeof(Page));
+        page = next;
+    }
+
+    // Unlink
+    _first = 0;
+    _totalBytes = 0;
+
+    _locker.Unlock();
+}
+
+void* ConcurrentArenaAllocator::Allocate(uint64 size, uint64 alignment)
+{
+RETRY:
+
+    // Check if the current page has some space left
+    Page* page = (Page*)Platform::AtomicRead(&_first);
+    if (page)
+    {
+        int64 offset = Platform::AtomicRead(&page->Offset);
+        int64 offsetAligned = Math::AlignUp(offset, (int64)alignment);
+        int64 end = offsetAligned + size;
+        if (end <= page->Size)
+        {
+            // Try to allocate within a page
+            if (Platform::InterlockedCompareExchange(&page->Offset, end, offset) != offset)
+            {
+                // Someone else changed allocated so retry (new offset might mismatch alignment)
+                goto RETRY;
+            }
+            Platform::InterlockedAdd(&_totalBytes, (int64)size);
+            return (byte*)page->Memory + offsetAligned;
+        }
+    }
+
+    // Page allocation is thread-synced
+    _locker.Lock();
+
+    // Check if page was unchanged by any other thread
+    if ((Page*)Platform::AtomicRead(&_first) == page)
+    {
+        uint64 pageSize = Math::Max<uint64>(_pageSize, size);
+#if COMPILE_WITH_PROFILER
+        ProfilerMemory::OnGroupUpdate(ProfilerMemory::Groups::MallocArena, (int64)pageSize, 1);
+#endif
+        page = (Page*)(_allocate1 ? _allocate1(sizeof(Page), alignof(Page)) : _allocate2(sizeof(Page)));
+        page->Memory = _allocate1 ? _allocate1(pageSize, 16) : _allocate2(pageSize);
+        page->Next = (Page*)_first;
+        page->Offset = 0;
+        page->Size = (int64)pageSize;
+        Platform::AtomicStore(&_first, (intptr)page);
+    }
+
+    _locker.Unlock();
+
+    // Use a single cde for allocation
+    goto RETRY;
+}