From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761394AbXGYK0V (ORCPT ); Wed, 25 Jul 2007 06:26:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757185AbXGYK0O (ORCPT ); Wed, 25 Jul 2007 06:26:14 -0400 Received: from one.firstfloor.org ([213.235.205.2]:44125 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756844AbXGYK0N (ORCPT ); Wed, 25 Jul 2007 06:26:13 -0400 Date: Wed, 25 Jul 2007 12:26:08 +0200 From: Andi Kleen To: Benjamin Herrenschmidt Cc: Andi Kleen , Peter Zijlstra , Andrew Morton , Ingo Molnar , linux-kernel@vger.kernel.org, Hugh Dickins Subject: Re: [patch] mm: reduce pagetable-freeing latencies Message-ID: <20070725102608.GB9045@one.firstfloor.org> References: <20070724083855.GA858@elte.hu> <20070724015441.8604d85d.akpm@linux-foundation.org> <1185270045.5439.249.camel@localhost.localdomain> <1185312559.5439.276.camel@localhost.localdomain> <1185345850.8197.64.camel@twins> <20070725094605.GA9045@one.firstfloor.org> <1185358093.5439.325.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1185358093.5439.325.camel@localhost.localdomain> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > Plan is fixed array or 4 or maybe 8 entries (pointers), that shouldn't > be -too- bad. The code path I'm a bit worried about is Yep. > unmap_mapping_ranges() which goes into zapping page tables from deep > within filesystems. Your aim is to conserve stack space? The worst case has to work without overflow anyways, so using VLAs don't help you. Just allocate the largest size you can safely afford. This is also easier to test; if it is too large it is better when the overflow triggers always. They are more useful in user space with larger stacks when you don't know the maximum size. -Andi