From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id 5F39A6B004D for ; Tue, 10 Nov 2009 17:45:14 -0500 (EST) Date: Tue, 10 Nov 2009 14:44:38 -0800 From: Andrew Morton Subject: Re: [MM] Make mm counters per cpu instead of atomic V2 Message-Id: <20091110144438.dbab0ba8.akpm@linux-foundation.org> In-Reply-To: <20091106101106.8115e0f1.kamezawa.hiroyu@jp.fujitsu.com> References: <20091104234923.GA25306@redhat.com> <20091106101106.8115e0f1.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: Christoph Lameter , Dave Jones , "hugh.dickins@tiscali.co.uk" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Tejun Heo List-ID: On Fri, 6 Nov 2009 10:11:06 +0900 KAMEZAWA Hiroyuki wrote: > On Thu, 5 Nov 2009 10:36:06 -0500 (EST) > Christoph Lameter wrote: > > > From: Christoph Lameter > > Subject: Make mm counters per cpu V2 > > > > Changing the mm counters to per cpu counters is possible after the introduction > > of the generic per cpu operations (currently in percpu and -next). > > > > With that the contention on the counters in mm_struct can be avoided. The > > USE_SPLIT_PTLOCKS case distinction can go away. Larger SMP systems do not > > need to perform atomic updates to mm counters anymore. Various code paths > > can be simplified since per cpu counter updates are fast and batching > > of counter updates is no longer needed. > > > > One price to pay for these improvements is the need to scan over all percpu > > counters when the actual count values are needed. > > > > V1->V2 > > - Remove useless and buggy per cpu counter initialization. > > alloc_percpu already zeros the values. > > > > Signed-off-by: Christoph Lameter > > > Thanks. My small concern is read-side. Me too. For example, with 1000 possible CPUs (possible, not present and not online), and 1000 processes, ps(1) will have to wallow through a million cachelines in task_statm(). And then we have get_mm_rs(), which now will hit 1000 cachelines. And get_mm_rs() is called (via account_user_time()->acct_update_integrals()) from the clock tick. Adding a thousand cache misses to the timer interrupt is the sort of thing which makes people unhappy? -- 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