staging: zcache: add TODO file

Add zcache TODO file

Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/zcache/TODO

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+
+** ZCACHE PLAN FOR PROMOTION FROM STAGING **
+
+Last updated: Feb 13, 2013
+
+PLAN STEPS
+
+1. merge zcache and ramster to eliminate horrible code duplication
+2. converge on a predictable, writeback-capable allocator
+3. use debugfs instead of sysfs (per akpm feedback in 2011)
+4. zcache side of cleancache/mm WasActive patch
+5. zcache side of frontswap exclusive gets
+6. zcache must be able to writeback to physical swap disk
+    (per Andrea Arcangeli feedback in 2011)
+7. implement adequate policy for writeback
+8. frontswap/cleancache work to allow zcache to be loaded
+    as a module
+9. get core mm developer to review
+10. incorporate feedback from review
+11. get review/acks from 1-2 additional mm developers
+12. incorporate any feedback from additional mm reviews
+13. propose location/file-naming in mm tree
+14. repeat 9-13 as necessary until akpm is happy and merges
+
+STATUS/OWNERSHIP
+
+1. DONE as part of "new" zcache; in staging/zcache for 3.9
+2. DONE as part of "new" zcache (cf zbud.[ch]); in staging/zcache for 3.9
+    (this was the core of the zcache1 vs zcache2 flail)
+3. DONE as part of "new" zcache; in staging/zcache for 3.9
+4. DONE (w/caveats) as part of "new" zcache; per cleancache performance
+    feedback see https://lkml.org/lkml/2011/8/17/351, in
+    staging/zcache for 3.9; dependent on proposed mm patch, see
+    https://lkml.org/lkml/2012/1/25/300 
+5. DONE as part of "new" zcache; performance tuning only,
+    in staging/zcache for 3.9; dependent on frontswap patch
+    merged in 3.7 (33c2a174)
+6. DONE (w/caveats), prototyped as part of "new" zcache, had
+    bad memory leak; reimplemented to use sjennings clever tricks
+    and proposed mm patches with new version in staging/zcache
+    for 3.9, see https://lkml.org/lkml/2013/2/6/437;
+7. PROTOTYPED as part of "new" zcache; in staging/zcache for 3.9;
+    needs more review (plan to discuss at LSF/MM 2013)
+8. IN PROGRESS; owned by Konrad Wilk; v2 recently posted
+   http://lkml.org/lkml/2013/2/1/542
+9. IN PROGRESS; owned by Konrad Wilk; Mel Gorman provided
+   great feedback in August 2012 (unfortunately of "old"
+   zcache)
+10. Konrad posted series of fixes (that now need rebasing)
+    https://lkml.org/lkml/2013/2/1/566 
+11. NOT DONE; owned by Konrad Wilk
+12. TBD (depends on quantity of feedback)
+13. PROPOSED; one suggestion proposed by Dan; needs more ideas/feedback
+14. TBD (depends on feedback)
+
+WHO NEEDS TO AGREE
+
+Not sure.  Seth Jennings is now pursuing a separate but semi-parallel
+track.  Akpm clearly has to approve for any mm merge to happen.  Minchan
+Kim has interest but may be happy if/when zram is merged into mm.  Konrad
+Wilk may be maintainer if akpm decides compression is maintainable
+separately from the rest of mm.  (More LSF/MM 2013 discussion.)
+
+ZCACHE FUTURE NEW FUNCTIONALITY
+
+A. Support zsmalloc as an alternative high-density allocator
+    (See https://lkml.org/lkml/2013/1/23/511)
+B. Support zero-filled pages more efficiently
+C. Possibly support three zbuds per pageframe when space allows