[Feature]add MT2731_MP2_MR2_SVN388 baseline version
Change-Id: Ief04314834b31e27effab435d3ca8ba33b499059
diff --git a/src/kernel/linux/v4.14/Documentation/vm/page_frags b/src/kernel/linux/v4.14/Documentation/vm/page_frags
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+Page fragments
+--------------
+
+A page fragment is an arbitrary-length arbitrary-offset area of memory
+which resides within a 0 or higher order compound page. Multiple
+fragments within that page are individually refcounted, in the page's
+reference counter.
+
+The page_frag functions, page_frag_alloc and page_frag_free, provide a
+simple allocation framework for page fragments. This is used by the
+network stack and network device drivers to provide a backing region of
+memory for use as either an sk_buff->head, or to be used in the "frags"
+portion of skb_shared_info.
+
+In order to make use of the page fragment APIs a backing page fragment
+cache is needed. This provides a central point for the fragment allocation
+and tracks allows multiple calls to make use of a cached page. The
+advantage to doing this is that multiple calls to get_page can be avoided
+which can be expensive at allocation time. However due to the nature of
+this caching it is required that any calls to the cache be protected by
+either a per-cpu limitation, or a per-cpu limitation and forcing interrupts
+to be disabled when executing the fragment allocation.
+
+The network stack uses two separate caches per CPU to handle fragment
+allocation. The netdev_alloc_cache is used by callers making use of the
+__netdev_alloc_frag and __netdev_alloc_skb calls. The napi_alloc_cache is
+used by callers of the __napi_alloc_frag and __napi_alloc_skb calls. The
+main difference between these two calls is the context in which they may be
+called. The "netdev" prefixed functions are usable in any context as these
+functions will disable interrupts, while the "napi" prefixed functions are
+only usable within the softirq context.
+
+Many network device drivers use a similar methodology for allocating page
+fragments, but the page fragments are cached at the ring or descriptor
+level. In order to enable these cases it is necessary to provide a generic
+way of tearing down a page cache. For this reason __page_frag_cache_drain
+was implemented. It allows for freeing multiple references from a single
+page via a single call. The advantage to doing this is that it allows for
+cleaning up the multiple references that were added to a page in order to
+avoid calling get_page per allocation.
+
+Alexander Duyck, Nov 29, 2016.