make balloon pages movable by compaction

Memory fragmentation introduced by ballooning might reduce significantly the number of 2MB contiguous memory blocks that can be used within a guest, thus imposing performance penalties associated with the reduced number of transparent huge pages that could be used by the guest workload.

This patch-set follows the main idea discussed at 2012 LSFMMS session:
"Ballooning for transparent huge pages" -- http://lwn.net/Articles/490114/
to introduce the required changes to the virtio_balloon driver, as well as the changes to the core compaction & migration bits, in order to make those subsystems aware of ballooned pages and allow memory balloon pages become movable within a guest, thus avoiding the aforementioned fragmentation issue

Following are numbers that prove this patch benefits on allowing compaction to be more effective at memory ballooned guests.

Results for STRESS-HIGHALLOC benchmark, from Mel Gorman's mmtests suite, running on a 4gB RAM KVM guest which was ballooning 512mB RAM in 64mB chunks, at every minute (inflating/deflating), while test was running:

===BEGIN stress-highalloc

STRESS-HIGHALLOC

                 highalloc-3.7     highalloc-3.7
                     rc4-clean         rc4-patch
Pass 1          55.00 ( 0.00%)    62.00 ( 7.00%)
Pass 2          54.00 ( 0.00%)    62.00 ( 8.00%)
while Rested    75.00 ( 0.00%)    80.00 ( 5.00%)

MMTests Statistics: duration

                 3.7         3.7
           rc4-clean   rc4-patch
User         1207.59     1207.46
System       1300.55     1299.61
Elapsed      2273.72     2157.06

MMTests Statistics: vmstat

                                3.7         3.7
                          rc4-clean   rc4-patch

Page Ins 3581516 2374368
Page Outs 11148692 10410332
Swap Ins 80 47
Swap Outs 3641 476
Direct pages scanned 37978 33826

Kswapd pages scanned        1828245     1342869
Kswapd pages reclaimed      1710236     1304099

Direct pages reclaimed 32207 31005
Kswapd efficiency 93% 97%
Kswapd velocity 804.077 622.546
Direct efficiency 84% 91%
Direct velocity 16.703 15.682
Percentage direct scans 2% 2%

Page writes by reclaim        79252        9704
Page writes file              75611        9228

Page writes anon 3641 476
Page reclaim immediate 16764 11014
Page rescued immediate 0 0
Slabs scanned 2171904 2152448
Direct inode steals 385 2261
Kswapd inode steals 659137 609670
Kswapd skipped wait 1 69

THP fault alloc                 546         631
THP collapse alloc              361         339
THP splits                      259         263
THP fault fallback               98          50
THP collapse fail                20          17
Compaction stalls               747         499
Compaction success              244         145
Compaction failures             503         354

Compaction pages moved 370888 474837
Compaction move failure 77378 65259

===END stress-highalloc

Rafael Aquini (7):
mm: adjust address_space_operations.migratepage() return code
mm: redefine address_space.assoc_mapping
mm: introduce a common interface for balloon pages mobility
mm: introduce compaction and migration for ballooned pages
virtio_balloon: introduce migration primitives to balloon pages
mm: introduce putback_movable_pages()
mm: add vm event counters for balloon pages compaction

 drivers/virtio/virtio_balloon.c    | 139 +++++++++++++++--
 fs/buffer.c                        |  12 +-
 fs/gfs2/glock.c                    |   2 +-
 fs/hugetlbfs/inode.c               |   4 +-
 fs/inode.c                         |   2 +-
 fs/nilfs2/page.c                   |   2 +-
 include/linux/balloon_compaction.h | 263 ++++++++++++++++++++++++++++++++
 include/linux/fs.h                 |   2 +-
 include/linux/migrate.h            |  19 +++
 include/linux/pagemap.h            |  16 ++
 include/linux/vm_event_item.h      |   7 +-
 mm/Kconfig                         |  15 ++
 mm/Makefile                        |   3 +-
 mm/balloon_compaction.c            | 304 +++++++++++++++++++++++++++++++++++++
 mm/compaction.c                    |  27 +++-
 mm/migrate.c                       |  86 ++++++++---
 mm/page_alloc.c                    |   2 +-
 mm/vmstat.c                        |   9 +-
 18 files changed, 862 insertions(+), 52 deletions(-)
 create mode 100644 include/linux/balloon_compaction.h
 create mode 100644 mm/balloon_compaction.c

Change log:
v12:
* Address last suggestions on sorting the barriers usage out (Mel Gorman);
* Fix reported build breakages for CONFIG_BALLOON_COMPACTION=n (Andrew Morton);
* Enhance commentary on the locking scheme used for balloon page compaction;
* Move all the 'balloon vm_event counter' changes to PATCH 07;
v11:
* Address AKPM's last review suggestions;
* Extend the balloon compaction common API and simplify its usage at driver;
* Minor nitpicks on code commentary;
v10:
* Adjust leak_balloon() wait_event logic to make a clear locking scheme (MST);
* Drop the RCU protection approach for dereferencing balloon's page->mapping;
* Minor nitpitcks on code commentaries (MST);
v9:
* Adjust rcu_dereference usage to leverage page lock protection (Paul, Peter);
* Enhance doc on compaction interface introduced to balloon driver (Michael);
* Fix issue with isolated pages breaking leak_balloon() logics (Michael);
v8:
* introduce a common MM interface for balloon driver page compaction (Michael);
* remove the global state preventing multiple balloon device support (Michael);
* introduce RCU protection/syncrhonization to balloon page->mapping (Michael);
v7:
* fix a potential page leak case at 'putback_balloon_page' (Mel);
* adjust vm-events-counter patch and remove its drop-on-merge message (Rik);
* add 'putback_movable_pages' to avoid hacks on 'putback_lru_pages' (Minchan);
v6:
* rename 'is_balloon_page()' to 'movable_balloon_page()' (Rik);
v5:
* address Andrew Morton's review comments on the patch series;
* address a couple extra nitpick suggestions on PATCH 01 (Minchan);
v4:
* address Rusty Russel's review comments on PATCH 02;
* re-base virtio_balloon patch on 9c378abc5c0c6fc8e3acf5968924d274503819b3;
V3:
* address reviewers nitpick suggestions on PATCH 01 (Mel, Minchan);
V2:
* address Mel Gorman's review comments on PATCH 01;

1.7.11.7

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