From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public•gmane.org (Eric W. Biederman)
To: Sasha Levin <levinsasha928-Re5JQEeQqe8AvxtiuMwx3w@public•gmane.org>
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Subject: Re: [PATCH 02/16] user_ns: use new hashtable implementation
Date: Tue, 14 Aug 2012 20:13:01 -0700 [thread overview]
Message-ID: <87obmchmpu.fsf@xmission.com> (raw)
In-Reply-To: <502AFCD5.6070104-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> (Sasha Levin's message of "Wed, 15 Aug 2012 03:35:17 +0200")
Sasha Levin <levinsasha928-Re5JQEeQqe8AvxtiuMwx3w@public•gmane.org> writes:
> On 08/15/2012 03:08 AM, Eric W. Biederman wrote:
>>> I can offer the following: I'll write a small module that will hash 1...10000
>>> > into a hashtable which uses 7 bits (just like user_ns) and post the distribution
>>> > we'll get.
>> That won't hurt. I think 1-100 then 1000-1100 may actually be more
>> representative. Not that I would mind seeing the larger range.
>> Especially since I am in the process of encouraging the use of more
>> uids.
>>
>
> Alrighty, the results are in (numbers are objects in bucket):
>
> For the 0...10000 range:
>
> Average: 78.125
> Std dev: 1.4197704151
> Min: 75
> Max: 80
>
>
> For the 1...100 range:
>
> Average: 0.78125
> Std dev: 0.5164613088
> Min: 0
> Max: 2
>
>
> For the 1000...1100 range:
>
> Average: 0.7890625
> Std dev: 0.4964812206
> Min: 0
> Max: 2
>
>
> Looks like hash_32 is pretty good with small numbers.
Yes hash_32 seems reasonable for the uid hash. With those long hash
chains I wouldn't like to be on a machine with 10,000 processes with
each with a different uid, and a processes calling setuid in the fast
path.
The uid hash that we are playing with is one that I sort of wish that
the hash table could grow in size, so that we could scale up better.
Aw well. Most of the time we only have a very small number of uids
in play, so it doesn't matter at this point.
Eric
next prev parent reply other threads:[~2012-08-15 3:13 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-14 16:24 [PATCH 00/16] generic hashtable implementation Sasha Levin
2012-08-14 16:24 ` [PATCH 02/16] user_ns: use new " Sasha Levin
2012-08-14 23:52 ` Eric W. Biederman
[not found] ` <87txw5hw0s.fsf-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2012-08-15 0:47 ` Sasha Levin
[not found] ` <502AF184.4010907-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2012-08-15 1:08 ` Eric W. Biederman
2012-08-15 1:35 ` Sasha Levin
[not found] ` <502AFCD5.6070104-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2012-08-15 3:13 ` Eric W. Biederman [this message]
2012-08-15 3:31 ` Mathieu Desnoyers
2012-08-15 13:40 ` Sasha Levin
[not found] ` <87obmchmpu.fsf-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2012-08-15 8:46 ` David Laight
[not found] ` <AE90C24D6B3A694183C094C60CF0A2F6026B6FB5-CgBM+Bx2aUAnGFn1LkZF6NBPR1lH4CV8@public.gmane.org>
2012-08-16 14:28 ` Mathieu Desnoyers
2012-08-14 16:24 ` [PATCH 03/16] mm,ksm: " Sasha Levin
[not found] ` <1344961490-4068-1-git-send-email-levinsasha928-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2012-08-14 16:24 ` [PATCH 01/16] hashtable: introduce a small and naive hashtable Sasha Levin
[not found] ` <1344961490-4068-2-git-send-email-levinsasha928-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2012-08-14 23:25 ` NeilBrown
[not found] ` <20120815092523.00a909ef-wvvUuzkyo1EYVZTmpyfIwg@public.gmane.org>
2012-08-15 0:24 ` Sasha Levin
2012-08-15 0:28 ` Tejun Heo
2012-08-14 16:24 ` [PATCH 04/16] workqueue: use new hashtable implementation Sasha Levin
2012-08-14 16:24 ` [PATCH 05/16] mm/huge_memory: " Sasha Levin
2012-08-14 16:24 ` [PATCH 06/16] tracepoint: " Sasha Levin
2012-08-14 16:24 ` [PATCH 08/16] block, elevator: " Sasha Levin
2012-08-14 16:24 ` [PATCH 09/16] SUNRPC/cache: " Sasha Levin
2012-08-14 16:24 ` [PATCH 10/16] dlm: " Sasha Levin
2012-08-14 16:24 ` [PATCH 11/16] net, l2tp: " Sasha Levin
2012-08-14 16:24 ` [PATCH 12/16] dm: " Sasha Levin
2012-08-14 16:24 ` [PATCH 13/16] lockd: " Sasha Levin
2012-08-14 16:24 ` [PATCH 15/16] openvswitch: " Sasha Levin
2012-08-14 16:24 ` [PATCH 16/16] tracing output: " Sasha Levin
2012-08-14 16:24 ` [PATCH 07/16] net,9p: " Sasha Levin
2012-08-14 16:24 ` [PATCH 14/16] net,rds: " Sasha Levin
2012-08-14 18:16 ` [PATCH 00/16] generic " J. Bruce Fields
-- strict thread matches above, loose matches on Subject: below --
2012-08-19 0:52 [PATCH v2 " Sasha Levin
2012-08-19 0:52 ` [PATCH 02/16] user_ns: use new " Sasha Levin
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