drivers/md/persistent-data/dm-transaction-manager.c: rename HASH_SIZE

Fix the warning:

  drivers/md/persistent-data/dm-transaction-manager.c:28:1: warning: "HASH_SIZE" redefined
  In file included from include/linux/elevator.h:5,
                   from include/linux/blkdev.h:216,
                   from drivers/md/persistent-data/dm-block-manager.h:11,
                   from drivers/md/persistent-data/dm-transaction-manager.h:10,
                   from drivers/md/persistent-data/dm-transaction-manager.c:6:
  include/linux/hashtable.h:22:1: warning: this is the location of the previous definition

Cc: Alasdair Kergon <agk@redhat.com>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
memcg, oom: provide more precise dump info while memcg oom happening

Currently when a memcg oom is happening the oom dump messages is still
global state and provides few useful info for users.  This patch prints
more pointed memcg page statistics for memcg-oom and take hierarchy into
consideration:

Based on Michal's advice, we take hierarchy into consideration: supppose
we trigger an OOM on A's limit

        root_memcg
            |
            A (use_hierachy=1)
           / \
          B   C
          |
          D
then the printed info will be:

  Memory cgroup stats for /A:...
  Memory cgroup stats for /A/B:...
  Memory cgroup stats for /A/C:...
  Memory cgroup stats for /A/B/D:...

Following are samples of oom output:

(1) Before change:

    mal-80 invoked oom-killer:gfp_mask=0xd0, order=0, oom_score_adj=0
    mal-80 cpuset=/ mems_allowed=0
    Pid: 2976, comm: mal-80 Not tainted 3.7.0+ #10
    Call Trace:
     [<ffffffff8167fbfb>] dump_header+0x83/0x1ca
     ..... (call trace)
     [<ffffffff8168a818>] page_fault+0x28/0x30
                             <<<<<<<<<<<<<<<<<<<<< memcg specific information
    Task in /A/B/D killed as a result of limit of /A
    memory: usage 101376kB, limit 101376kB, failcnt 57
    memory+swap: usage 101376kB, limit 101376kB, failcnt 0
    kmem: usage 0kB, limit 9007199254740991kB, failcnt 0
                             <<<<<<<<<<<<<<<<<<<<< print per cpu pageset stat
    Mem-Info:
    Node 0 DMA per-cpu:
    CPU    0: hi:    0, btch:   1 usd:   0
    ......
    CPU    3: hi:    0, btch:   1 usd:   0
    Node 0 DMA32 per-cpu:
    CPU    0: hi:  186, btch:  31 usd: 173
    ......
    CPU    3: hi:  186, btch:  31 usd: 130
                             <<<<<<<<<<<<<<<<<<<<< print global page state
    active_anon:92963 inactive_anon:40777 isolated_anon:0
     active_file:33027 inactive_file:51718 isolated_file:0
     unevictable:0 dirty:3 writeback:0 unstable:0
     free:729995 slab_reclaimable:6897 slab_unreclaimable:6263
     mapped:20278 shmem:35971 pagetables:5885 bounce:0
     free_cma:0
                             <<<<<<<<<<<<<<<<<<<<< print per zone page state
    Node 0 DMA free:15836kB ... all_unreclaimable? no
    lowmem_reserve[]: 0 3175 3899 3899
    Node 0 DMA32 free:2888564kB ... all_unrelaimable? no
    lowmem_reserve[]: 0 0 724 724
    lowmem_reserve[]: 0 0 0 0
    Node 0 DMA: 1*4kB (U) ... 3*4096kB (M) = 15836kB
    Node 0 DMA32: 41*4kB (UM) ... 702*4096kB (MR) = 2888316kB
    120710 total pagecache pages
    0 pages in swap cache
                             <<<<<<<<<<<<<<<<<<<<< print global swap cache stat
    Swap cache stats: add 0, delete 0, find 0/0
    Free swap  = 499708kB
    Total swap = 499708kB
    1040368 pages RAM
    58678 pages reserved
    169065 pages shared
    173632 pages non-shared
    [ pid ]   uid  tgid total_vm      rss nr_ptes swapents oom_score_adj name
    [ 2693]     0  2693     6005     1324      17        0             0 god
    [ 2754]     0  2754     6003     1320      16        0             0 god
    [ 2811]     0  2811     5992     1304      18        0             0 god
    [ 2874]     0  2874     6005     1323      18        0             0 god
    [ 2935]     0  2935     8720     7742      21        0             0 mal-30
    [ 2976]     0  2976    21520    17577      42        0             0 mal-80
    Memory cgroup out of memory: Kill process 2976 (mal-80) score 665 or sacrifice child
    Killed process 2976 (mal-80) total-vm:86080kB, anon-rss:69964kB, file-rss:344kB

We can see that messages dumped by show_free_areas() are longsome and can
provide so limited info for memcg that just happen oom.

(2) After change
    mal-80 invoked oom-killer: gfp_mask=0xd0, order=0, oom_score_adj=0
    mal-80 cpuset=/ mems_allowed=0
    Pid: 2704, comm: mal-80 Not tainted 3.7.0+ #10
    Call Trace:
     [<ffffffff8167fd0b>] dump_header+0x83/0x1d1
     .......(call trace)
     [<ffffffff8168a918>] page_fault+0x28/0x30
    Task in /A/B/D killed as a result of limit of /A
                             <<<<<<<<<<<<<<<<<<<<< memcg specific information
    memory: usage 102400kB, limit 102400kB, failcnt 140
    memory+swap: usage 102400kB, limit 102400kB, failcnt 0
    kmem: usage 0kB, limit 9007199254740991kB, failcnt 0
    Memory cgroup stats for /A: cache:32KB rss:30984KB mapped_file:0KB swap:0KB inactive_anon:6912KB active_anon:24072KB inactive_file:32KB active_file:0KB unevictable:0KB
    Memory cgroup stats for /A/B: cache:0KB rss:0KB mapped_file:0KB swap:0KB inactive_anon:0KB active_anon:0KB inactive_file:0KB active_file:0KB unevictable:0KB
    Memory cgroup stats for /A/C: cache:0KB rss:0KB mapped_file:0KB swap:0KB inactive_anon:0KB active_anon:0KB inactive_file:0KB active_file:0KB unevictable:0KB
    Memory cgroup stats for /A/B/D: cache:32KB rss:71352KB mapped_file:0KB swap:0KB inactive_anon:6656KB active_anon:64696KB inactive_file:16KB active_file:16KB unevictable:0KB
    [ pid ]   uid  tgid total_vm      rss nr_ptes swapents oom_score_adj name
    [ 2260]     0  2260     6006     1325      18        0             0 god
    [ 2383]     0  2383     6003     1319      17        0             0 god
    [ 2503]     0  2503     6004     1321      18        0             0 god
    [ 2622]     0  2622     6004     1321      16        0             0 god
    [ 2695]     0  2695     8720     7741      22        0             0 mal-30
    [ 2704]     0  2704    21520    17839      43        0             0 mal-80
    Memory cgroup out of memory: Kill process 2704 (mal-80) score 669 or sacrifice child
    Killed process 2704 (mal-80) total-vm:86080kB, anon-rss:71016kB, file-rss:340kB

This version provides more pointed info for memcg in "Memory cgroup stats
for XXX" section.

Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/memcontrol.c: convert printk(KERN_FOO) to pr_foo()

Acked-by: Sha Zhengju <handai.szj@taobao.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/hugetlb.c: convert to pr_foo()

Cc: Michal Hocko <mhocko@suse.cz>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
CMA: make putback_lru_pages() call conditional

As per documentation and other places calling putback_lru_pages(),
putback_lru_pages() is called on error only.  Make the CMA code behave
consistently.

[akpm@linux-foundation.org: remove a test-n-branch in the wrapup code]
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: memcg: only evict file pages when we have plenty

Commit e9868505987a ("mm, vmscan: only evict file pages when we have
plenty") makes a point of not going for anonymous memory while there is
still enough inactive cache around.

The check was added only for global reclaim, but it is just as useful to
reduce swapping in memory cgroup reclaim:

    200M-memcg-defconfig-j2

                                     vanilla                   patched
    Real time              454.06 (  +0.00%)         453.71 (  -0.08%)
    User time              668.57 (  +0.00%)         668.73 (  +0.02%)
    System time            128.92 (  +0.00%)         129.53 (  +0.46%)
    Swap in               1246.80 (  +0.00%)         814.40 ( -34.65%)
    Swap out              1198.90 (  +0.00%)         827.00 ( -30.99%)
    Pages allocated   16431288.10 (  +0.00%)    16434035.30 (  +0.02%)
    Major faults           681.50 (  +0.00%)         593.70 ( -12.86%)
    THP faults             237.20 (  +0.00%)         242.40 (  +2.18%)
    THP collapse           241.20 (  +0.00%)         248.50 (  +3.01%)
    THP splits             157.30 (  +0.00%)         161.40 (  +2.59%)

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Satoru Moriya <satoru.moriya@hds.com>
Cc: Simon Jeons <simon.jeons@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: vmscan: save work scanning (almost) empty LRU lists

In certain cases (kswapd reclaim, memcg target reclaim), a fixed minimum
amount of pages is scanned from the LRU lists on each iteration, to make
progress.

Do not make this minimum bigger than the respective LRU list size,
however, and save some busy work trying to isolate and reclaim pages
that are not there.

Empty LRU lists are quite common with memory cgroups in NUMA
environments because there exists a set of LRU lists for each zone for
each memory cgroup, while the memory of a single cgroup is expected to
stay on just one node.  The number of expected empty LRU lists is thus

  memcgs * (nodes - 1) * lru types

Each attempt to reclaim from an empty LRU list does expensive size
comparisons between lists, acquires the zone's lru lock etc.  Avoid
that.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Satoru Moriya <satoru.moriya@hds.com>
Cc: Simon Jeons <simon.jeons@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: vmscan: clarify how swappiness, highest priority, memcg interact

A swappiness of 0 has a slightly different meaning for global reclaim
(may swap if file cache really low) and memory cgroup reclaim (never
swap, ever).

In addition, global reclaim at highest priority will scan all LRU lists
equal to their size and ignore other balancing heuristics.  UNLESS
swappiness forbids swapping, then the lists are balanced based on recent
reclaim effectiveness.  UNLESS file cache is running low, then anonymous
pages are force-scanned.

This (total mess of a) behaviour is implicit and not obvious from the
way the code is organized.  At least make it apparent in the code flow
and document the conditions.  It will be it easier to come up with sane
semantics later.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Satoru Moriya <satoru.moriya@hds.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Simon Jeons <simon.jeons@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: vmscan: improve comment on low-page cache handling

Fix comment style and elaborate on why anonymous memory is force-scanned
when file cache runs low.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Satoru Moriya <satoru.moriya@hds.com>
Cc: Simon Jeons <simon.jeons@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: vmscan: clean up get_scan_count()

Reclaim pressure balance between anon and file pages is calculated
through a tuple of numerators and a shared denominator.

Exceptional cases that want to force-scan anon or file pages configure
the numerators and denominator such that one list is preferred, which is
not necessarily the most obvious way:

    fraction[0] = 1;
    fraction[1] = 0;
    denominator = 1;
    goto out;

Make this easier by making the force-scan cases explicit and use the
fractionals only in case they are calculated from reclaim history.

[akpm@linux-foundation.org: avoid using unintialized_var()]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Satoru Moriya <satoru.moriya@hds.com>
Cc: Simon Jeons <simon.jeons@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: vmscan: compaction works against zones, not lruvecs

The restart logic for when reclaim operates back to back with compaction
is currently applied on the lruvec level.  But this does not make sense,
because the container of interest for compaction is a zone as a whole,
not the zone pages that are part of a certain memory cgroup.

Negative impact is bounded.  For one, the code checks that the lruvec
has enough reclaim candidates, so it does not risk getting stuck on a
condition that can not be fulfilled.  And the unfairness of hammering on
one particular memory cgroup to make progress in a zone will be
amortized by the round robin manner in which reclaim goes through the
memory cgroups.  Still, this can lead to unnecessary allocation
latencies when the code elects to restart on a hard to reclaim or small
group when there are other, more reclaimable groups in the zone.

Move this logic to the zone level and restart reclaim for all memory
cgroups in a zone when compaction requires more free pages from it.

[akpm@linux-foundation.org: no need for min_t]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Satoru Moriya <satoru.moriya@hds.com>
Cc: Simon Jeons <simon.jeons@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: reduce rmap overhead for ex-KSM page copies created on swap faults

When ex-KSM pages are faulted from swap cache, the fault handler is not
capable of re-establishing anon_vma-spanning KSM pages.  In this case, a
copy of the page is created instead, just like during a COW break.

These freshly made copies are known to be exclusive to the faulting VMA
and there is no reason to go look for this page in parent and sibling
processes during rmap operations.

Use page_add_new_anon_rmap() for these copies.  This also puts them on
the proper LRU lists and marks them SwapBacked, so we can get rid of
doing this ad-hoc in the KSM copy code.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Simon Jeons <simon.jeons@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Satoru Moriya <satoru.moriya@hds.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/page_alloc.c:__setup_per_zone_wmarks: make min_pages unsigned long

`int' is an inappropriate type for a number-of-pages counter.

While we're there, use the clamp() macro.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Satoru Moriya <satoru.moriya@hds.com>
Cc: Simon Jeons <simon.jeons@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/vmscan.c:__zone_reclaim(): replace max_t() with max()

"mm: vmscan: save work scanning (almost) empty LRU lists" made
SWAP_CLUSTER_MAX an unsigned long.

Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Satoru Moriya <satoru.moriya@hds.com>
Cc: Simon Jeons <simon.jeons@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: compaction: do not accidentally skip pageblocks in the migrate scanner

Compaction uses the ALIGN macro incorrectly with the migrate scanner by
adding pageblock_nr_pages to a PFN.  It happened to work when initially
implemented as the starting PFN was also aligned but with caching
restarts and isolating in smaller chunks this is no longer always true.

The impact is that the migrate scanner scans outside its current
pageblock.  As pfn_valid() is still checked properly it does not cause
any failure and the impact of the bug is that in some cases it will scan
more than necessary when it crosses a page boundary but by no more than
COMPACT_CLUSTER_MAX.  It is highly unlikely this is even measurable but
it's still wrong so this patch addresses the problem.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/huge_memory.c: use new hashtable implementation

Switch hugemem to use the new hashtable implementation.  This reduces
the amount of generic unrelated code in the hugemem.

This also removes the dymanic allocation of the hash table.  The upside
is that we save a pointer dereference when accessing the hashtable, but
we lose 8KB if CONFIG_TRANSPARENT_HUGEPAGE is enabled but the processor
doesn't support hugepages.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/ksm.c: use new hashtable implementation

Switch ksm to use the new hashtable implementation.  This reduces the
amount of generic unrelated code in the ksm module.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
memcg,vmscan: do not break out targeted reclaim without reclaimed pages

Targeted (hard resp soft) reclaim has traditionally tried to scan one
group with decreasing priority until nr_to_reclaim (SWAP_CLUSTER_MAX
pages) is reclaimed or all priorities are exhausted.  The reclaim is
then retried until the limit is met.

This approach, however, doesn't work well with deeper hierarchies where
groups higher in the hierarchy do not have any or only very few pages
(this usually happens if those groups do not have any tasks and they
have only re-parented pages after some of their children is removed).
Those groups are reclaimed with decreasing priority pointlessly as there
is nothing to reclaim from them.

An easiest fix is to break out of the memcg iteration loop in
shrink_zone only if the whole hierarchy has been visited or sufficient
pages have been reclaimed.  This is also more natural because the
reclaimer expects that the hierarchy under the given root is reclaimed.
As a result we can simplify the soft limit reclaim which does its own
iteration.

[yinghan@google.com: break out of the hierarchy loop only if nr_reclaimed exceeded nr_to_reclaim]
[akpm@linux-foundation.org: use conventional comparison order]
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Reported-by: Ying Han <yinghan@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Glauber Costa <glommer@parallels.com>
Cc: Li Zefan <lizefan@huawei.com>
Signed-off-by: Ying Han <yinghan@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: make madvise(MADV_WILLNEED) support swap file prefetch

Make madvise(MADV_WILLNEED) support swap file prefetch.  If memory is
swapout, this syscall can do swapin prefetch.  It has no impact if the
memory isn't swapout.

[akpm@linux-foundation.org: fix CONFIG_SWAP=n build]
[sasha.levin@oracle.com: fix BUG on madvise early failure]
Signed-off-by: Shaohua Li <shli@fusionio.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: compaction: make __compact_pgdat() and compact_pgdat() return void

These functions always return 0.  Formalise this.

Cc: Jason Liu <r64343@freescale.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>