caller can then report those stats to the user (perhaps via ethtool,
debugfs, etc.). See below for an example usage of this API.
+DMA sync
+--------
+Driver is always responsible for syncing the pages for the CPU.
+Drivers may choose to take care of syncing for the device as well
+or set the ``PP_FLAG_DMA_SYNC_DEV`` flag to request that pages
+allocated from the page pool are already synced for the device.
+
+If ``PP_FLAG_DMA_SYNC_DEV`` is set, the driver must inform the core what portion
+of the buffer has to be synced. This allows the core to avoid syncing the entire
+page when the drivers knows that the device only accessed a portion of the page.
+
+Most drivers will reserve headroom in front of the frame. This part
+of the buffer is not touched by the device, so to avoid syncing
+it drivers can set the ``offset`` field in struct page_pool_params
+appropriately.
+
+For pages recycled on the XDP xmit and skb paths the page pool will
+use the ``max_len`` member of struct page_pool_params to decide how
+much of the page needs to be synced (starting at ``offset``).
+When directly freeing pages in the driver (page_pool_put_page())
+the ``dma_sync_size`` argument specifies how much of the buffer needs
+to be synced.
+
+If in doubt set ``offset`` to 0, ``max_len`` to ``PAGE_SIZE`` and
+pass -1 as ``dma_sync_size``. That combination of arguments is always
+correct.
+
+Note that the syncing parameters are for the entire page.
+This is important to remember when using fragments (``PP_FLAG_PAGE_FRAG``),
+where allocated buffers may be smaller than a full page.
+Unless the driver author really understands page pool internals
+it's recommended to always use ``offset = 0``, ``max_len = PAGE_SIZE``
+with fragmented page pools.
+
Stats API and structures
------------------------
If the kernel is configured with ``CONFIG_PAGE_POOL_STATS=y``, the API