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 45B7D6B0044 for ; Thu, 3 May 2012 16:27:02 -0400 (EDT) Message-ID: <4FA2EA08.9030109@redhat.com> Date: Thu, 03 May 2012 16:26:48 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH 1/1] mlock: split the shmlock_user_lock spinlock into per user_struct spinlock References: <1336066477-3964-1-git-send-email-rajman.mekaco@gmail.com> <1336073474.6509.2.camel@twins> In-Reply-To: <1336073474.6509.2.camel@twins> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: rajman mekaco , Ingo Molnar , Paul Gortmaker , Andrew Morton , KOSAKI Motohiro , Minchan Kim , Christoph Lameter , linux-kernel@vger.kernel.org, linux-mm@kvack.org On 05/03/2012 03:31 PM, Peter Zijlstra wrote: > On Thu, 2012-05-03 at 23:04 +0530, rajman mekaco wrote: >> The user_shm_lock and user_shm_unlock functions use a single global >> spinlock for protecting the user->locked_shm. > > Are you very sure its only protecting user state? This changelog doesn't > convince me you've gone through everything and found it good. > >> This is an overhead for multiple CPUs calling this code even if they >> are having different user_struct. >> >> Remove the global shmlock_user_lock and introduce and use a new >> spinlock inside of the user_struct structure. > > While I don't immediately see anything wrong with it, I doubt its > useful. What workload run with enough users that this makes a difference > one way or another? When running with containers and/or LXC, I believe that each UID in each container gets its own user_struct, but you do raise a good question - what user programs call mlock anyway, and how often? -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org