From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with ESMTP id 1FEE08D0040 for ; Wed, 30 Mar 2011 22:33:15 -0400 (EDT) Date: Wed, 30 Mar 2011 19:34:04 -0700 From: Andrew Morton Subject: Re: [PATCH]mmap: improve scalability for updating vm_committed_as Message-Id: <20110330193404.9525b4e9.akpm@linux-foundation.org> In-Reply-To: <1301533003.3981.75.camel@sli10-conroe> References: <1301447847.3981.49.camel@sli10-conroe> <20110330155114.fa47dd9d.akpm@linux-foundation.org> <1301533003.3981.75.camel@sli10-conroe> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Shaohua Li Cc: linux-mm , lkml , Andi Kleen , Rik van Riel , Hugh Dickins On Thu, 31 Mar 2011 08:56:43 +0800 Shaohua Li wrote: > > This is a big change, and it wasn't even changelogged. It's > > potentially a tremendous increase in the expense of a read from > > /proc/meminfo, which is a file that lots of tools will be polling. > > Many of those tools we don't even know about or have access to. > Assume we don't read /proc/meminfo too often. That's a poor assumption. top(1) and vmstat(8) read it, for a start. There will be zillions of locally-developed monitoring tools which read meminfo. Now, it could be that something under meminfo reads _already_ does a massive walk across all CPUs. If so then we'll have already trained people to avoid reading /proc/meminfo and this change might be acceptable. But if this isn't the case then it's quite likely that this change will hurt some people quite a lot. And, unfortunately, the sort of people who we will hurt tend to be people who don't run our stuff until a long time (years) after we wrote it. By which time it's going to be quite expensive to get a fix down the chain and into their hands. -- 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