From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx192.postini.com [74.125.245.192]) by kanga.kvack.org (Postfix) with SMTP id E03EE6B0044 for ; Tue, 14 Aug 2012 23:13:25 -0400 (EDT) From: ebiederm@xmission.com (Eric W. Biederman) 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> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [PATCH 02/16] user_ns: use new hashtable implementation Sender: owner-linux-mm@kvack.org List-ID: 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 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org