[RFC PATCH v2 0/4] mm: reclaim zbud pages on migration and compaction

[Krzysztof Kozlowski <k.kozlowski@samsung.com>]

Hi,

Currently zbud pages are not movable and they cannot be allocated from CMA
region. These patches try to address the problem by:
1. Adding a new form of reclaim of zbud pages.
2. Reclaiming zbud pages during migration and compaction.
3. Allocating zbud pages with __GFP_RECLAIMABLE flag.

This reclaim process is different than zbud_reclaim_page(). It acts more
like swapoff() by trying to unuse pages stored in zbud page and bring
them back to memory. The standard zbud_reclaim_page() on the other hand
tries to write them back.

One of patches introduces PageZbud() function which identifies zbud pages
my page->_mapcount. Dave Hansen proposed aliasing PG_zbud=PG_slab but in
such case patch would be more intrusive.

Any ideas for a better solution are welcome.

TODO-s:
1. Migrate zbud pages directly instead of reclaiming.

Changes since v1:
1. Rebased against v3.11-rc4-103-g6c2580c.
2. Remove rebalance_lists() to fix reinserting zbud page after zbud_free.
   This function was added because similar code was present in
   zbud_free/zbud_alloc/zbud_reclaim_page but it turns out that there
   is no benefit in generalizing this code.
   (suggested by Seth Jennings)
3. Remove BUG_ON checks for first/last chunks during free and reclaim.
   (suggested by Seth Jennings)
4. Use page->_mapcount==-127 instead of new PG_zbud flag.
   (suggested by Dave Hansen)
5. Fix invalid dereference of pointer to compact_control in page_alloc.c.
6. Fix lost return value in try_to_unuse() in swapfile.c (this fixes
   hang when swapoff was interrupted e.g. by CTRL+C).


Best regards,
Krzysztof Kozlowski


Krzysztof Kozlowski (4):
  zbud: use page ref counter for zbud pages
  mm: split code for unusing swap entries from try_to_unuse
  mm: use mapcount for identifying zbud pages
  mm: reclaim zbud pages on migration and compaction

 include/linux/mm.h       |   23 +++
 include/linux/swapfile.h |    2 +
 include/linux/zbud.h     |   11 +-
 mm/compaction.c          |   20 ++-
 mm/internal.h            |    1 +
 mm/page_alloc.c          |    6 +
 mm/swapfile.c            |  356 ++++++++++++++++++++++++----------------------
 mm/zbud.c                |  247 +++++++++++++++++++++++---------
 mm/zswap.c               |   57 +++++++-
 9 files changed, 476 insertions(+), 247 deletions(-)

-- 
1.7.9.5

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