Merge branch 'akpm' (patches from Andrew)

- use_hierarchy is on by default and the cgroup file for the flag is

  not created.

- The original lower boundary, the soft limit, is defined as a limit

  that is per default unset.  As a result, the set of cgroups that

  global reclaim prefers is opt-in, rather than opt-out.  The costs

  for optimizing these mostly negative lookups are so high that the

  implementation, despite its enormous size, does not even provide the

  basic desirable behavior.  First off, the soft limit has no

  hierarchical meaning.  All configured groups are organized in a

  global rbtree and treated like equal peers, regardless where they

  are located in the hierarchy.  This makes subtree delegation

  impossible.  Second, the soft limit reclaim pass is so aggressive

  that it not just introduces high allocation latencies into the

  system, but also impacts system performance due to overreclaim, to

  the point where the feature becomes self-defeating.

  The memory.low boundary on the other hand is a top-down allocated

  reserve.  A cgroup enjoys reclaim protection when it and all its

  ancestors are below their low boundaries, which makes delegation of

  subtrees possible.  Secondly, new cgroups have no reserve per

  default and in the common case most cgroups are eligible for the

  preferred reclaim pass.  This allows the new low boundary to be

  efficiently implemented with just a minor addition to the generic

  reclaim code, without the need for out-of-band data structures and

  reclaim passes.  Because the generic reclaim code considers all

  cgroups except for the ones running low in the preferred first

  reclaim pass, overreclaim of individual groups is eliminated as

  well, resulting in much better overall workload performance.

- The original high boundary, the hard limit, is defined as a strict

  limit that can not budge, even if the OOM killer has to be called.

  But this generally goes against the goal of making the most out of

  the available memory.  The memory consumption of workloads varies

  during runtime, and that requires users to overcommit.  But doing

  that with a strict upper limit requires either a fairly accurate

  prediction of the working set size or adding slack to the limit.

  Since working set size estimation is hard and error prone, and

  getting it wrong results in OOM kills, most users tend to err on the

  side of a looser limit and end up wasting precious resources.

  The memory.high boundary on the other hand can be set much more

  conservatively.  When hit, it throttles allocations by forcing them

  into direct reclaim to work off the excess, but it never invokes the

  OOM killer.  As a result, a high boundary that is chosen too

  aggressively will not terminate the processes, but instead it will

  lead to gradual performance degradation.  The user can monitor this

  and make corrections until the minimal memory footprint that still

  gives acceptable performance is found.

  In extreme cases, with many concurrent allocations and a complete

  breakdown of reclaim progress within the group, the high boundary

  can be exceeded.  But even then it's mostly better to satisfy the

  allocation from the slack available in other groups or the rest of

  the system than killing the group.  Otherwise, memory.max is there

  to limit this type of spillover and ultimately contain buggy or even

  malicious applications.

- The original control file names are unwieldy and inconsistent in

  many different ways.  For example, the upper boundary hit count is

  exported in the memory.failcnt file, but an OOM event count has to

  be manually counted by listening to memory.oom_control events, and

  lower boundary / soft limit events have to be counted by first

  setting a threshold for that value and then counting those events.

  Also, usage and limit files encode their units in the filename.

  That makes the filenames very long, even though this is not

  information that a user needs to be reminded of every time they type

  out those names.

  To address these naming issues, as well as to signal clearly that

  the new interface carries a new configuration model, the naming

  conventions in it necessarily differ from the old interface.

- The original limit files indicate the state of an unset limit with a

  Very High Number, and a configured limit can be unset by echoing -1

  into those files.  But that very high number is implementation and

  architecture dependent and not very descriptive.  And while -1 can

  be understood as an underflow into the highest possible value, -2 or

  -10M etc. do not work, so it's not consistent.

  memory.low, memory.high, and memory.max will use the string

  "infinity" to indicate and set the highest possible value.

5. Planned Changes

  3.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm

  3.7   /proc/<pid>/task/<tid>/children - Information about task children

  3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file

  3.9   /proc/<pid>/map_files - Information about memory mapped files

  4	Configuring procfs

  4.1	Mount options

	with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'

	still exhibits timer's remaining time.

3.9	/proc/<pid>/map_files - Information about memory mapped files

---------------------------------------------------------------------

This directory contains symbolic links which represent memory mapped files

the process is maintaining.  Example output:

     | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so

     | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so

     | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so

     | ...

     | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1

     | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls

The name of a link represents the virtual memory bounds of a mapping, i.e.

vm_area_struct::vm_start-vm_area_struct::vm_end.

The main purpose of the map_files is to retrieve a set of memory mapped

files in a fast way instead of parsing /proc/<pid>/maps or

/proc/<pid>/smaps, both of which contain many more records.  At the same

time one can open(2) mappings from the listings of two processes and

comparing their inode numbers to figure out which anonymous memory areas

are actually shared.

------------------------------------------------------------------------------

Configuring procfs

------------------------------------------------------------------------------

oom_dump_tasks

Enables a system-wide task dump (excluding kernel threads) to be

produced when the kernel performs an OOM-killing and includes such

information as pid, uid, tgid, vm size, rss, nr_ptes, swapents,

oom_score_adj score, and name.  This is helpful to determine why the

OOM killer was invoked, to identify the rogue task that caused it,

and to determine why the OOM killer chose the task it did to kill.

Enables a system-wide task dump (excluding kernel threads) to be produced

when the kernel performs an OOM-killing and includes such information as

pid, uid, tgid, vm size, rss, nr_ptes, nr_pmds, swapents, oom_score_adj

score, and name.  This is helpful to determine why the OOM killer was

invoked, to identify the rogue task that caused it, and to determine why

the OOM killer chose the task it did to kill.

If this is set to zero, this information is suppressed.  On very

large systems with thousands of tasks it may not be feasible to dump

    20. NOPAGE

    21. KSM

    22. THP

    23. BALLOON

    24. ZERO_PAGE

Short descriptions to the page flags:

22. THP

    contiguous pages which construct transparent hugepages

23. BALLOON

    balloon compaction page

24. ZERO_PAGE

    zero page for pfn_zero or huge_zero page

    [IO related page flags]

 1. ERROR     IO error occurred

 3. UPTODATE  page has up-to-date data

#define PTRS_PER_PMD	(1UL << (PAGE_SHIFT-3))

#define PTRS_PER_PGD	(1UL << (PAGE_SHIFT-3))

#define USER_PTRS_PER_PGD	(TASK_SIZE / PGDIR_SIZE)

#define FIRST_USER_ADDRESS	0

#define FIRST_USER_ADDRESS	0UL

/* Number of pointers that fit on a page:  this will go away. */

#define PTRS_PER_PAGE	(1UL << (PAGE_SHIFT-3))