Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752199AbXJVXra (ORCPT ); Mon, 22 Oct 2007 19:47:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751065AbXJVXrT (ORCPT ); Mon, 22 Oct 2007 19:47:19 -0400 Received: from waste.org ([66.93.16.53]:35007 "EHLO waste.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750793AbXJVXrS (ORCPT ); Mon, 22 Oct 2007 19:47:18 -0400 Date: Mon, 22 Oct 2007 18:46:23 -0500 From: Matt Mackall To: Alan Cox Cc: Jeff Garzik , Linus Torvalds , Geert Uytterhoeven , Jens Axboe , Linux Kernel Development , mingo@elte.hu, Linux/m68k Subject: Re: [PATCH 09/10] Change table chaining layout Message-ID: <20071022234622.GT19691@waste.org> References: <1193076664-13652-1-git-send-email-jens.axboe@oracle.com> <1193076664-13652-10-git-send-email-jens.axboe@oracle.com> <20071022211617.31f5c63d@the-village.bc.nu> <471D145A.40904@garzik.org> <20071022214707.GJ17536@waste.org> <20071022235251.656b9cad@the-village.bc.nu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071022235251.656b9cad@the-village.bc.nu> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1304 Lines: 32 On Mon, Oct 22, 2007 at 11:52:51PM +0100, Alan Cox wrote: > On Mon, 22 Oct 2007 16:47:07 -0500 > Matt Mackall wrote: > > > On Mon, Oct 22, 2007 at 05:21:30PM -0400, Jeff Garzik wrote: > > > Alan Cox wrote: > > > >Why can't we just make the list one item longer than the entry count and > > > >stick a NULL on the end of it like normal people ? > > > > > > Certainly seems safer than the current "let's run off the end of the > > > list if anything bad happens" setup... And I do not think allocating > > > n+1 scatterlist entries will have much of a negative impact. > > > > It'll mean m-1 scatterlists fit on a slab. > > Is that really a credible space issue ? Yes. Especially if m is 2 or 1. A scatterlist on 64-bit x86 looks like it takes 32 bytes, which means 128 elements fit on a page. One more spills - ouch! But maybe chaining means this doesn't matter any more. Maybe we can even pick a nice moderate sg size and reduce the number of mempools we need for these things. -- Mathematics is the supreme nostalgia of our time. - 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/