linux-kernel - Re: [PATCH -mm 1/3] cgroup: use a hash table for css

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Date:	Thu, 03 Apr 2008 18:13:13 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	containers@...ts.linux-foundation.org,
	Paul Menage <menage@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -mm 1/3] cgroup: use a hash table for css_set finding

>>> +static struct hlist_head *css_set_hash(struct cgroup_subsys_state *css[])
>>> +{
>>> +	int i;
>>> +	int index;
>>> +	unsigned long tmp = 0UL;
>>> +
>>> +	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)
>>> +		tmp += (unsigned long)css[i];
>>> +
>> maybe css[i]'s lower 2-3 bits will be ignored. because thery are always 0.
>>
>> And I don't like "+" for hash. how about
>> ==
>> 	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)
>> 	unsigned long x;
>> 	x = (unsigned long)css[i];
>> 	tmp = (x >> 16) ^ (x & 0xffff)
>> ==
>> or some func, which uses full bits.
>>
> 
> I'm using hash_long(), which has been proved to be a good one. And I've tested
> css_set_hash(), I run the css_set benchmark with N == 1000, the for loop in
> find_existing_css_set() will break out within 10 iterations for most cases, 
> which is the expected result.
> 

I just revised the css_set_hash() a bit, and It turned out we can improve the
scalability.

Thanks, KAMEZAWA-san.
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