mm/swap: fix race on swap_info reuse between swapoff and swapon

Date	Thu, 09 Jan 2014 13:39:55 +0800

swapoff clear swap_info's SWP_USED flag prematurely and free its resources
after that. A concurrent swapon will reuse this swap_info while its previous
resources are not cleared completely.

These late freed resources are:
- p->percpu_cluster
- swap_cgroup_ctrl[type]
- block_device setting
- inode->i_flags &= ~S_SWAPFILE

This patch clear SWP_USED flag after all its resources freed, so that swapon
can reuse this swap_info by alloc_swap_info() safely.

Signed-off-by: Weijie Yang <weijie.yang@samsung.com>
Signed-off-by: Paul Reioux <reioux@gmail.com>

Conflicts:
	mm/swapfile.c
page_alloc: Make watermarks tunable separately

This patch introduces three new sysctls to /proc/sys/vm:
wmark_min_kbytes, wmark_low_kbytes and wmark_high_kbytes.

Each entry is used to compute watermark[min], watermark[low]
and watermark[high] for each zone.

These parameters are also updated when min_free_kbytes are
changed because originally they are set based on min_free_kbytes.
On the other hand, min_free_kbytes is updated when wmark_free_kbytes
changes.

By using the parameters one can adjust the difference among
watermark[min], watermark[low] and watermark[high] and as a result
one can tune the kernel reclaim behaviour to fit their requirement.

Signed-off-by: Satoru Moriya <satoru.moriya@hds.com>

modified and tuned for Hammerhead

Signed-off-by: Paul Reioux <reioux@gmail.com>

Conflicts:
	kernel/sysctl.c
	mm/page_alloc.c
sched/fair: Optimize find_busiest_queue()

Use for_each_cpu_and() and thereby avoid computing the capacity for
CPUs we know we're not interested in.

Reviewed-by: Paul Turner <pjt@google.com>
Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-lppceyv6kb3a19g8spmrn20b@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul Reioux <reioux@gmail.com>

backported for Linux 3.4

Conflicts:
	kernel/sched/fair.c
sched/fair: Optimize cgroup pick_next_task_fair()

Since commit 2f36825b1 ("sched: Next buddy hint on sleep and preempt
path") it is likely we pick a new task from the same cgroup, doing a put
and then set on all intermediate entities is a waste of time, so try to
avoid this.

Measured using:

  mount nodev /cgroup -t cgroup -o cpu
  cd /cgroup
  mkdir a; cd a
  mkdir b; cd b
  mkdir c; cd c
  echo $$ > tasks
  perf stat --repeat 10 -- taskset 1 perf bench sched pipe

PRE :      4.542422684 seconds time elapsed   ( +-  0.33% )
POST:      4.389409991 seconds time elapsed   ( +-  0.32% )

Which shows a significant improvement of ~3.5%

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/r/1328936700.2476.17.camel@laptop
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul Reioux <reioux@gmail.com>

Backported for Linux 3.4 kernel

Conflicts:
	kernel/sched/fair.c