===============
A memory pool is an allocator of a fixed-sized object.
-In the DPDK, it is identified by name and uses a ring to store free objects.
+In the DPDK, it is identified by name and uses a mempool handler to store free objects.
+The default mempool handler is ring based.
It provides some other optional services such as a per-core object cache and
an alignment helper to ensure that objects are padded to spread them equally on all DRAM or DDR3 channels.
-This library is used by the
-:ref:`Mbuf Library <Mbuf_Library>` and the
-:ref:`Environment Abstraction Layer <Environment_Abstraction_Layer>` (for logging history).
+This library is used by the :ref:`Mbuf Library <Mbuf_Library>`.
Cookies
-------
The command line must always have the number of memory channels specified for the processor.
-Examples of alignment for different DIMM architectures are shown in Figure 5 and Figure 6.
+Examples of alignment for different DIMM architectures are shown in
+:numref:`figure_memory-management` and :numref:`figure_memory-management2`.
-.. _pg_figure_5:
+.. _figure_memory-management:
-**Figure 5. Two Channels and Quad-ranked DIMM Example**
+.. figure:: img/memory-management.*
-.. image19_png has been replaced
+ Two Channels and Quad-ranked DIMM Example
-|memory-management|
In this case, the assumption is that a packet is 16 blocks of 64 bytes, which is not true.
The Intel® 5520 chipset has three channels, so in most cases,
no padding is required between objects (except for objects whose size are n x 3 x 64 bytes blocks).
-.. _pg_figure_6:
+.. _figure_memory-management2:
-**Figure 6. Three Channels and Two Dual-ranked DIMM Example**
+.. figure:: img/memory-management2.*
-.. image20_png has been replaced
+ Three Channels and Two Dual-ranked DIMM Example
-|memory-management2|
When creating a new pool, the user can specify to use this feature or not.
+.. _mempool_local_cache:
+
Local Cache
-----------
the speed at which a core can access its own cache for a specific memory pool without locks provides performance gains.
The cache is composed of a small, per-core table of pointers and its length (used as a stack).
-This cache can be enabled or disabled at creation of the pool.
+This internal cache can be enabled or disabled at creation of the pool.
The maximum size of the cache is static and is defined at compilation time (CONFIG_RTE_MEMPOOL_CACHE_MAX_SIZE).
-Figure 7 shows a cache in operation.
+:numref:`figure_mempool` shows a cache in operation.
+
+.. _figure_mempool:
+
+.. figure:: img/mempool.*
+
+ A mempool in Memory with its Associated Ring
+
+Alternatively to the internal default per-lcore local cache, an application can create and manage external caches through the ``rte_mempool_cache_create()``, ``rte_mempool_cache_free()`` and ``rte_mempool_cache_flush()`` calls.
+These user-owned caches can be explicitly passed to ``rte_mempool_generic_put()`` and ``rte_mempool_generic_get()``.
+The ``rte_mempool_default_cache()`` call returns the default internal cache if any.
+In contrast to the default caches, user-owned caches can be used by non-EAL threads too.
+
+Mempool Handlers
+------------------------
+
+This allows external memory subsystems, such as external hardware memory
+management systems and software based memory allocators, to be used with DPDK.
-.. _pg_figure_7:
+There are two aspects to a mempool handler.
-**Figure 7. A mempool in Memory with its Associated Ring**
+* Adding the code for your new mempool operations (ops). This is achieved by
+ adding a new mempool ops code, and using the ``MEMPOOL_REGISTER_OPS`` macro.
-.. image21_png has been replaced
+* Using the new API to call ``rte_mempool_create_empty()`` and
+ ``rte_mempool_set_ops_byname()`` to create a new mempool and specifying which
+ ops to use.
+
+Several different mempool handlers may be used in the same application. A new
+mempool can be created by using the ``rte_mempool_create_empty()`` function,
+then using ``rte_mempool_set_ops_byname()`` to point the mempool to the
+relevant mempool handler callback (ops) structure.
+
+Legacy applications may continue to use the old ``rte_mempool_create()`` API
+call, which uses a ring based mempool handler by default. These applications
+will need to be modified to use a new mempool handler.
+
+For applications that use ``rte_pktmbuf_create()``, there is a config setting
+(``RTE_MBUF_DEFAULT_MEMPOOL_OPS``) that allows the application to make use of
+an alternative mempool handler.
-|mempool|
Use Cases
---------
* :ref:`Environment Abstraction Layer <Environment_Abstraction_Layer>` , for logging service
* Any application that needs to allocate fixed-sized objects in the data plane and that will be continuously utilized by the system.
-
-.. |memory-management| image:: img/memory-management.*
-
-.. |memory-management2| image:: img/memory-management2.*
-
-.. |mempool| image:: img/mempool.*
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