make direct compaction more deterministic

This is mostly a followup to Michal's oom detection rework, which highlighted
the need for direct compaction to provide better feedback in reclaim/compaction
loop, so that it can reliably recognize when compaction cannot make further
progress, and allocation should invoke OOM killer or fail. We've discussed
this at LSF/MM [1] where I proposed expanding the async/sync migration mode
used in compaction to more general "priorities". This patchset adds one new
priority that just overrides all the heuristics and makes compaction fully
scan all zones. I don't currently think that we need more fine-grained
priorities, but we'll see. Other than that there's some smaller fixes and
cleanups, mainly related to the THP-specific hacks.

Testing/evaluation is pending, but I'm posting it now with hope to help the
discussions around oom detection rework. I also hope for testing the near-OOM
conditions, and the new priority level should also help hugetlbfs allocations
since they use __GFP_RETRY, and it has already been reported that ignoring
compaction heuristics helps these allocations.

The series is based on mmotm git [2] tag mmotm-2016-04-27-15-21-14.
First one needs to git revert the commit 69340d225e8d ("mm: use compaction
feedback for thp backoff conditions") which already happened in mmots.

[1] https://lwn.net/Articles/684611/
[2] git://git.kernel.org/pub/scm/linux/kernel/git/mhocko/mm.git

Hugh Dickins (1):
  mm, compaction: don't isolate PageWriteback pages in
    MIGRATE_SYNC_LIGHT mode

Vlastimil Babka (12):
  mm, page_alloc: set alloc_flags only once in slowpath
  mm, page_alloc: don't retry initial attempt in slowpath
  mm, page_alloc: restructure direct compaction handling in slowpath
  mm, page_alloc: make THP-specific decisions more generic
  mm, thp: remove __GFP_NORETRY from khugepaged and madvised allocations
  mm, compaction: introduce direct compaction priority
  mm, compaction: simplify contended compaction handling
  mm, compaction: make whole_zone flag ignore cached scanner positions
  mm, compaction: cleanup unused functions
  mm, compaction: add the ultimate direct compaction priority
  mm, compaction: more reliably increase direct compaction priority
  mm, compaction: fix and improve watermark handling

 include/linux/compaction.h |  32 +++----
 include/linux/gfp.h        |   3 +-
 include/linux/mm.h         |   2 +-
 mm/compaction.c            | 196 +++++++++++++++-------------------------
 mm/huge_memory.c           |   8 +-
 mm/internal.h              |  10 +--
 mm/page_alloc.c            | 220 +++++++++++++++++++++------------------------
 mm/page_isolation.c        |   2 +-
 8 files changed, 196 insertions(+), 277 deletions(-)

-- 
2.8.2

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