[Feature]add MT2731_MP2_MR2_SVN388 baseline version

Change-Id: Ief04314834b31e27effab435d3ca8ba33b499059
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+Overview:
+
+Zswap is a lightweight compressed cache for swap pages. It takes pages that are
+in the process of being swapped out and attempts to compress them into a
+dynamically allocated RAM-based memory pool.  zswap basically trades CPU cycles
+for potentially reduced swap I/O.  This trade-off can also result in a
+significant performance improvement if reads from the compressed cache are
+faster than reads from a swap device.
+
+NOTE: Zswap is a new feature as of v3.11 and interacts heavily with memory
+reclaim.  This interaction has not been fully explored on the large set of
+potential configurations and workloads that exist.  For this reason, zswap
+is a work in progress and should be considered experimental.
+
+Some potential benefits:
+* Desktop/laptop users with limited RAM capacities can mitigate the
+    performance impact of swapping.
+* Overcommitted guests that share a common I/O resource can
+    dramatically reduce their swap I/O pressure, avoiding heavy handed I/O
+    throttling by the hypervisor. This allows more work to get done with less
+    impact to the guest workload and guests sharing the I/O subsystem
+* Users with SSDs as swap devices can extend the life of the device by
+    drastically reducing life-shortening writes.
+
+Zswap evicts pages from compressed cache on an LRU basis to the backing swap
+device when the compressed pool reaches its size limit.  This requirement had
+been identified in prior community discussions.
+
+Zswap is disabled by default but can be enabled at boot time by setting
+the "enabled" attribute to 1 at boot time. ie: zswap.enabled=1.  Zswap
+can also be enabled and disabled at runtime using the sysfs interface.
+An example command to enable zswap at runtime, assuming sysfs is mounted
+at /sys, is:
+
+echo 1 > /sys/module/zswap/parameters/enabled
+
+When zswap is disabled at runtime it will stop storing pages that are
+being swapped out.  However, it will _not_ immediately write out or fault
+back into memory all of the pages stored in the compressed pool.  The
+pages stored in zswap will remain in the compressed pool until they are
+either invalidated or faulted back into memory.  In order to force all
+pages out of the compressed pool, a swapoff on the swap device(s) will
+fault back into memory all swapped out pages, including those in the
+compressed pool.
+
+Design:
+
+Zswap receives pages for compression through the Frontswap API and is able to
+evict pages from its own compressed pool on an LRU basis and write them back to
+the backing swap device in the case that the compressed pool is full.
+
+Zswap makes use of zpool for the managing the compressed memory pool.  Each
+allocation in zpool is not directly accessible by address.  Rather, a handle is
+returned by the allocation routine and that handle must be mapped before being
+accessed.  The compressed memory pool grows on demand and shrinks as compressed
+pages are freed.  The pool is not preallocated.  By default, a zpool of type
+zbud is created, but it can be selected at boot time by setting the "zpool"
+attribute, e.g. zswap.zpool=zbud.  It can also be changed at runtime using the
+sysfs "zpool" attribute, e.g.
+
+echo zbud > /sys/module/zswap/parameters/zpool
+
+The zbud type zpool allocates exactly 1 page to store 2 compressed pages, which
+means the compression ratio will always be 2:1 or worse (because of half-full
+zbud pages).  The zsmalloc type zpool has a more complex compressed page
+storage method, and it can achieve greater storage densities.  However,
+zsmalloc does not implement compressed page eviction, so once zswap fills it
+cannot evict the oldest page, it can only reject new pages.
+
+When a swap page is passed from frontswap to zswap, zswap maintains a mapping
+of the swap entry, a combination of the swap type and swap offset, to the zpool
+handle that references that compressed swap page.  This mapping is achieved
+with a red-black tree per swap type.  The swap offset is the search key for the
+tree nodes.
+
+During a page fault on a PTE that is a swap entry, frontswap calls the zswap
+load function to decompress the page into the page allocated by the page fault
+handler.
+
+Once there are no PTEs referencing a swap page stored in zswap (i.e. the count
+in the swap_map goes to 0) the swap code calls the zswap invalidate function,
+via frontswap, to free the compressed entry.
+
+Zswap seeks to be simple in its policies.  Sysfs attributes allow for one user
+controlled policy:
+* max_pool_percent - The maximum percentage of memory that the compressed
+    pool can occupy.
+
+The default compressor is lzo, but it can be selected at boot time by setting
+the “compressor” attribute, e.g. zswap.compressor=lzo.  It can also be changed
+at runtime using the sysfs "compressor" attribute, e.g.
+
+echo lzo > /sys/module/zswap/parameters/compressor
+
+When the zpool and/or compressor parameter is changed at runtime, any existing
+compressed pages are not modified; they are left in their own zpool.  When a
+request is made for a page in an old zpool, it is uncompressed using its
+original compressor.  Once all pages are removed from an old zpool, the zpool
+and its compressor are freed.
+
+A debugfs interface is provided for various statistic about pool size, number
+of pages stored, and various counters for the reasons pages are rejected.