template <class Alloc> class _OgreExport AllocatedObject
{
	public:
		void* operator new(size_t sz, const char* file, int line, const char* func)
		{
			return Alloc::allocateBytes(sz, file, line, func);
		}
		void* operator new(size_t sz)
		{
			return Alloc::allocateBytes(sz);
		}
		/// placement operator new
		void* operator new(size_t sz, void* ptr)
		{
			(void) sz;
			return ptr;
		}
		/// array operator new, with debug line info
		void* operator new[] ( size_t sz, const char* file, int line, const char* func )
		{
			return Alloc::allocateBytes(sz, file, line, func);
		}
		void* operator new[] ( size_t sz )
		{
			return Alloc::allocateBytes(sz);
		}
		.....
		..override delete
		.....
}

It use macro to choose policy, which looks like this

#elif OGRE_MEMORY_ALLOCATOR == OGRE_MEMORY_ALLOCATOR_NED
#  include "OgreMemoryNedAlloc.h"
namespace Ogre
{
	template <MemoryCategory Cat> class CategorisedAllocPolicy : public NedAllocPolicy{};
	template <MemoryCategory Cat, size_t align = 0> class CategorisedAlignAllocPolicy : public NedAlignedAllocPolicy<align>{};
}
#elif

As yo can see, the policy it self is a template, it takes a nontype argument  MemoryCategory which is defined as

enum MemoryCategory
	{
		/// General purpose
		MEMCATEGORY_GENERAL = 0,
		/// Geometry held in main memory
		MEMCATEGORY_GEOMETRY = 1, 
		/// Animation data like tracks, bone matrices
		MEMCATEGORY_ANIMATION = 2, 
		/// Nodes, control data
		MEMCATEGORY_SCENE_CONTROL = 3,
		/// Scene object instances
		MEMCATEGORY_SCENE_OBJECTS = 4,
		/// Other resources
		MEMCATEGORY_RESOURCE = 5,
		/// Scripting
		MEMCATEGORY_SCRIPTING = 6,
		/// Rendersystem structures
		MEMCATEGORY_RENDERSYS = 7,

		
		// sentinel value, do not use 
		MEMCATEGORY_COUNT = 8
	};

This is used to indicate the purse of a chunk of memory being used.These categories will be provided at allocation time in order to allow
the allocation policy to vary its behaviour if it wishes.

Then ogre define specific class allocator which looks like this:

typedef CategorisedAllocPolicy<Ogre::MEMCATEGORY_SCENE_OBJECTS> SceneObjAllocPolicy;
typedef AllocatedObject<SceneObjAllocPolicy> SceneObjAllocatedObject;
typedef SceneObjAllocatedObject		MovableAlloc;

class  MovableObject : <span style="font-family: Arial, Helvetica, sans-serif;">MovableAlloc</span>

Then you can use OGRE_NEW to allocate memory.

For primitive type you can use OGRE_NEW_T, It‘s defined as

OGRE_NEW_T(T, category) new (::Ogre::CategorisedAllocPolicy<category>::allocateBytes(sizeof(T))) T

Just a placement new.