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Subject[-mm][PATCH 0/5] mm: page reclaim throttle v6
Against: 2.6.25-mm1

changelog
========================================
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
The 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.
Today, 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 happend.

1. memory shortage happend.
2. many task call shrink_zone at the same time.
3. 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 various parameter of hackbench.

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

num_group vanilla with throttle
--------------------------------------------
80 26.22 24.97
85 27.31 25.94
90 29.23 26.77
95 30.73 28.40
100 32.02 30.62
105 33.97 31.93
110 35.37 33.19
115 36.96 33.68
120 74.05 36.25
125 41.07 39.30
130 86.92 45.74
135 234.62 45.99
140 291.95 57.82
145 425.35 70.31
150 766.92 113.28

Why this patch imrove performance?

vanilla kernel get unstable performance at swap happend.
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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