Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262854AbUKTC2o (ORCPT ); Fri, 19 Nov 2004 21:28:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262838AbUKTC1E (ORCPT ); Fri, 19 Nov 2004 21:27:04 -0500 Received: from smtp205.mail.sc5.yahoo.com ([216.136.129.95]:57479 "HELO smtp205.mail.sc5.yahoo.com") by vger.kernel.org with SMTP id S262857AbUKTCZq (ORCPT ); Fri, 19 Nov 2004 21:25:46 -0500 Message-ID: <419EAB21.8020207@yahoo.com.au> Date: Sat, 20 Nov 2004 13:25:37 +1100 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.2) Gecko/20040820 Debian/1.7.2-4 X-Accept-Language: en MIME-Version: 1.0 To: William Lee Irwin III CC: Linus Torvalds , Christoph Lameter , akpm@osdl.org, Benjamin Herrenschmidt , Hugh Dickins , linux-mm@kvack.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: page fault scalability patch V11 [0/7]: overview References: <419D581F.2080302@yahoo.com.au> <419D5E09.20805@yahoo.com.au> <1100848068.25520.49.camel@gaston> <20041120020306.GA2714@holomorphy.com> In-Reply-To: <20041120020306.GA2714@holomorphy.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1590 Lines: 44 William Lee Irwin III wrote: > On Fri, Nov 19, 2004 at 11:59:03AM -0800, Linus Torvalds wrote: > >>You could also make "rss" be a _signed_ integer per-thread. >>When unmapping a page, you decrement one of the threads that shares the mm >>(doesn't matter which - which is why the per-thread rss may go negative), >>and when mapping a page you increment it. >>Then, anybody who actually wants a global rss can just iterate over >>threads and add it all up. If you do it under the mmap_sem, it's stable, >>and if you do it outside the mmap_sem it's imprecise but stable in the >>long term (ie errors never _accumulate_, like the non-atomic case will >>do). >>Does anybody care enough? Maybe, maybe not. It certainly sounds a hell of >>a lot better than the periodic scan. > > > Unprivileged triggers for full-tasklist scans are NMI oops material. > What about pushing the per-thread rss delta back into the global atomic rss counter in each schedule()? Pros: This would take the task exiting problem into its stride as a matter of course. Single atomic read to get rss. Cons: would just be moving the atomic op somewhere else if we don't get many page faults per schedule. Not really nice dependancies. Assumes schedule (not context switch) must occur somewhat regularly. At present this is not true for SCHED_FIFO tasks. Too nasty? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/