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Subject[PATCH 0/5] page reclaim throttle v7
Hi

I post latest version of page reclaim patch series.

This patch is holding up very well under usex stress test
over 24+ hours :)


Against: 2.6.26-rc2-mm1


changelog
========================================
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. fix the bug of incorrect OOM killer>>

if do following commanc, 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. the last task can't isolate any page from LRU.
5. it cause reclaim failure.
6. it cause OOM killer.

my patch is directly solution for that problem.


<<2. performance improvement>>
I mesure RvR Split LRU series + page reclaim throttle series performance by hackbench.

result number mean seconds (i.e. smaller is better)


+ split_lru improvement
num_group 2.6.26-rc2-mm1 + throttle ratio
-----------------------------------------------------------------
100 28.383 28.247
110 31.237 30.83
120 33.282 33.473
130 36.530 37.356
140 101.041 44.873 >200%
150 795.020 96.265 >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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