[PATCH -mm 0/3] cgroup: use hash table for css_set

[Li Zefan <lizf@cn.fujitsu.com>]

When we attach a process to a different cgroup, the css_set linked-list
will be run through to find a suitable existing css_set to use. This
patch set uses a hash table for better performance.

As we add the hash table, we can totally remove the css_set linked-list.
When we have to run through the linked-list, we can run through the
hash table instead.

I tested the following benmarks:

For N in 1, 5, 10, 50, 100, 500, 1000, create N cgroups with one sleeping
task in each, and then move an additional task through each cgroup in
turn.

Here is a test result:

N	Loop	orig - Time(s)	hash - Time(s)
----------------------------------------------
1	10000	1.201231728	1.196311177
5	2000	1.065743872	1.040566424
10	1000	0.991054735	0.986876440
50	200	0.976554203	0.969608733
100	100	0.998504680	0.969218270
500	20	1.157347764	0.962602963
1000	10	1.619521852	1.085140172

Those patches are based on 2.6.25-rc5-mm1.

Regards,
Li Zefan