From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759563AbXGOSdj (ORCPT ); Sun, 15 Jul 2007 14:33:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752079AbXGOSda (ORCPT ); Sun, 15 Jul 2007 14:33:30 -0400 Received: from main.gmane.org ([80.91.229.2]:43919 "EHLO ciao.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751772AbXGOSda (ORCPT ); Sun, 15 Jul 2007 14:33:30 -0400 X-Injected-Via-Gmane: http://gmane.org/ To: linux-kernel@vger.kernel.org From: =?iso-8859-1?Q?M=E5ns_Rullg=E5rd?= Subject: Re: [PATCH][RFC] 4K stacks default, not a debug thing any more...? Date: Sun, 15 Jul 2007 19:32:58 +0100 Message-ID: References: <8FO1e-2jW-35@gated-at.bofh.it> <8FYWD-2eS-7@gated-at.bofh.it> <8GdsH-8dc-13@gated-at.bofh.it> <8Ghmx-60z-17@gated-at.bofh.it> <8Gj55-hJ-5@gated-at.bofh.it> <8GkNo-2Vb-1@gated-at.bofh.it> <8GtnN-7TG-23@gated-at.bofh.it> <8GVjY-PL-25@gated-at.bofh.it> <1184520917.3153.4.camel@laptopd505.fenrus.org> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit X-Complaints-To: usenet@sea.gmane.org X-Gmane-NNTP-Posting-Host: agrajag.inprovide.com User-Agent: Gnus/5.1008 (Gnus v5.10.8) XEmacs/21.4.20 (Double Solitaire, linux) Cancel-Lock: sha1:lM3fTeAVt/qyhRS8y/tt+qiNgIA= Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Arjan van de Ven writes: > On Sun, 2007-07-15 at 19:17 +0200, Bodo Eggert wrote: >> Matt Mackall wrote: >> > On Fri, Jul 13, 2007 at 03:20:54PM +0200, Rene Herman wrote: >> >> >> As far as I'm aware, the actual reason for 4K stacks is that after the >> >> system has been up and running for some time getting "1 physically >> >> contiguous pages" becomes significantly easier than 2 which wouldn't be >> >> arbitrary. >> > >> > If there are exactly two free pages in the system, the odds of them >> > being buddies (ie adjacent AND properly aligned) is quite small. The >> > available page pool has to grow quite a bit before the availability of >> > order-1 page pairs approaches 100%. >> >> If there are exactly two free pages in a system, the odds of starting any >> program are not very good. You'll have to swap, and if you do, you can swap >> two more pages in order to free enough RAM for the stack. > > even if you have several thousand pages the odds aren't good; or rather, > they start out reasonably ok until something starts eating very > deliberately at the 8k pages pool, for example the new app creating > about 10 threads.... > > The 4K issue is "tricky", only a few selected workload/compiler combos > seem to hit the dirt, yet distros like Fedora and RHEL use 4K stacks > since forever, and if it gave massive problems they wouldn't do that. > On the upside, especially on very-threaded workloads, it helps > reliability and the VM a lot... I guess no Fedora users run md+lvm+xfs then. That combination has quite reliably crashed any 4k-stack kernel I've ever cared to try. -- Måns Rullgård mans@mansr.com