From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx197.postini.com [74.125.245.197]) by kanga.kvack.org (Postfix) with SMTP id 9CB2E6B0070 for ; Wed, 15 Aug 2012 09:39:33 -0400 (EDT) Received: by obhx4 with SMTP id x4so2708167obh.14 for ; Wed, 15 Aug 2012 06:39:32 -0700 (PDT) Message-ID: <502BA6B4.9020106@gmail.com> Date: Wed, 15 Aug 2012 15:40:04 +0200 From: Sasha Levin MIME-Version: 1.0 Subject: Re: [PATCH 02/16] user_ns: use new hashtable implementation 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> <87obmchmpu.fsf@xmission.com> <20120815033155.GA32653@Krystal> In-Reply-To: <20120815033155.GA32653@Krystal> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mathieu Desnoyers Cc: "Eric W. Biederman" , 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, 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 On 08/15/2012 05:31 AM, Mathieu Desnoyers wrote: > * Eric W. Biederman (ebiederm@xmission.com) wrote: >> 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. > > Hi Eric, > > If you want to try out something that has more features than a basic > hash table, already exists and is available for you to play with, you > might want to have a look at the RCU lock-free resizable hash table. > It's initially done in userspace, but shares the same RCU semantic as > the kernel, and has chunk-based kernel-friendly index backends (thanks > to Lai Jiangshan), very useful to integrate with the kernel page > allocator. I'm guessing that once this static hashtable is stable, a DEFINE_DYNAMIC_HASHTABLE() will get introduced which will evolve into something similar to what Mathieu has pointed out in the urcu. -- 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