From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753180Ab2HODN1 (ORCPT ); Tue, 14 Aug 2012 23:13:27 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:46299 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751313Ab2HODNZ (ORCPT ); Tue, 14 Aug 2012 23:13:25 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Sasha Levin Cc: torvalds@linux-foundation.org, tj@kernel.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, paul.gortmaker@windriver.com, davem@davemloft.net, rostedt@goodmis.org, mingo@elte.hu, aarcange@redhat.com, ericvh@gmail.com, netdev@vger.kernel.org, josh@joshtriplett.org, eric.dumazet@gmail.com, mathieu.desnoyers@efficios.com, axboe@kernel.dk, agk@redhat.com, dm-devel@redhat.com, neilb@suse.de, ccaulfie@redhat.com, teigland@redhat.com, Trond.Myklebust@netapp.com, bfields@fieldses.org, fweisbec@gmail.com, jesse@nicira.com, venkat.x.venkatsubra@oracle.com, ejt@redhat.com, snitzer@redhat.com, edumazet@google.com, linux-nfs@vger.kernel.org, dev@openvswitch.org, rds-devel@oss.oracle.com, lw@cn.fujitsu.com References: <1344961490-4068-1-git-send-email-levinsasha928@gmail.com> <1344961490-4068-3-git-send-email-levinsasha928@gmail.com> <87txw5hw0s.fsf@xmission.com> <502AF184.4010907@gmail.com> <87393phshy.fsf@xmission.com> <502AFCD5.6070104@gmail.com> Date: Tue, 14 Aug 2012 20:13:01 -0700 In-Reply-To: <502AFCD5.6070104@gmail.com> (Sasha Levin's message of "Wed, 15 Aug 2012 03:35:17 +0200") Message-ID: <87obmchmpu.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=;;;mid=;;;hst=in01.mta.xmission.com;;;ip=98.207.153.68;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+Ckg0PDEd41XS1+XSlu63leXKVjMlog1g= X-SA-Exim-Connect-IP: 98.207.153.68 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 1.5 XMNoVowels Alpha-numberic number with no vowels * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -3.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% * [score: 0.0000] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa06 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_TooManySym_01 4+ unique symbols in subject * 0.1 XMSolicitRefs_0 Weightloss drug X-Spam-DCC: XMission; sa06 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Sasha Levin X-Spam-Relay-Country: Subject: Re: [PATCH 02/16] user_ns: use new hashtable implementation X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Fri, 06 Aug 2010 16:31:04 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sasha Levin 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