flashcache-wt is a simple, non-persistent write-through and write-around
flashcache.

It is a separate code base from flashcache (which is write back only).

Notes :
-----
1) flashcache-wt is non persistent, which means that on a cache remove 
(or a reboot), you will lose the cache entirely. Since the cache is 
write-through/write-around, this will not result in any data loss.
2) Built on 2.6.18, .20, .27-.32 successfully. Tested on .18, .20, .27 
and .32 successfully.

Building flashcache-wt :
----------------------
opsdev209.snc1.facebook.com> make KERNEL_TREE=<Base of kernel tree>

Creating a flashcache-wt volume :
-------------------------------
flashcache_wt_create : Create a new flashcache-wt volume.

flashcache_wt_create [-r] [-s cache size] [-b block size] cachedevname ssd_devname disk_devname

Very similar to flashcache_create.

Note : The default is to create the cache write-through. Use the -r option to create the
cache write-around.

Removing a flashcache-wt volume :
----------------------------
Use dmsetup remove to remove a flashcache-wt volume.

Example:
dmsetup remove cachedev

Cache Stats :
===========
Use 'dmsetup status' for cache statistics.

'dmsetup table' also dumps a number of cache related statistics.

Examples :
dmsetup status cachedev
dmsetup table cachedev

Cache Blocksize Selection
-------------------------
4KB cache blocks are suitable for the vast majority of the cases.

Also see the flashcache-sa-guide for more discussion on this.