[PATCH 0/3] page reclaim throttle v8

[kosaki.motohiro@jp.fujitsu.com]

-- 

Hi,

This patch is latest page reclaim throttle patch.



changelog
========================================
  v7 -> v8
     o remove Kconfig parameter.
     o merge throtte patch and sysctl parameter adding patch.
     o add some patch description.

  v6 -> v7
     o rebase to 2.6.26-rc2-mm1
     o get_vm_stat: make cpu-unplug safety.
     o mark vm_max_nr_task_per_zone __read_mostly.
     o add check __GFP_FS, __GFP_IO for avoid deadlock.
     o fixed compile error on x86_64.

  v5 -> v6
     o rebase to 2.6.25-mm1
     o use PGFREE statics instead wall time.
     o separate function type change patch and introduce throttle patch.

  v4 -> v5
     o rebase to 2.6.25-rc8-mm1

  v3 -> v4:
     o fixed recursive shrink_zone problem.
     o add last_checked variable in shrink_zone for 
       prevent corner case regression.

  v2 -> v3:
     o use wake_up() instead wake_up_all()
     o max reclaimers can be changed Kconfig option and sysctl.
     o some cleanups

  v1 -> v2:
     o make per zone throttle 



background
=====================================
current VM implementation doesn't has limit of # of parallel reclaim.
when heavy workload, it bring to 2 bad things
  - heavy lock contention
  - unnecessary swap out

at end of last year, KAMEZAWA Hiroyuki proposed the patch of page 
reclaim throttle and explain it improve reclaim time.
	http://marc.info/?l=linux-mm&m=119667465917215&w=2

but unfortunately it works only memcgroup reclaim.
since, I implement it again for support global reclaim and mesure it.


benefit
=====================================
<<1. fixed a bug of incorrect OOM killer>>

if do following command, sometimes OOM killer happened.
(OOM happend about 10%)

 $ ./hackbench 125 process 1000

because following bad scenario is happend.

   1. memory shortage happend.
   2. many task call shrink_zone() at the same time.
   3. thus, All page are isolated from LRU at the same time.
   4. if another task call shrink_zone(), it can't isolate any page from LRU.
   5. Then, it cause reclaim failure and OOM killer.

my patch is solution for that problem directly.


<<2. performance improvement>>
I mesured performance by hackbench.
result number mean seconds (i.e. smaller is better)


                                              improvement
   num_group   2.6.26-rc8-mm1   + throttle    ratio
   -----------------------------------------------------------------
   100          39.262           39.035
   110          42.051           46.697
   120          45.153           45.685
   130          73.325           57.183
   140          87.830           63.791       
   150         947.493          113.231       >800%



Why this patch imrove performance?

vanilla kernel get unstable performance at swap happend because
unnecessary swap out happend freqently.
this patch doesn't improvement best case, but be able to prevent worst case.
thus, The average performance of hackbench increase largely.


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