Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754038AbXJWJ4p (ORCPT ); Tue, 23 Oct 2007 05:56:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753696AbXJWJ4f (ORCPT ); Tue, 23 Oct 2007 05:56:35 -0400 Received: from brick.kernel.dk ([87.55.233.238]:6447 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753683AbXJWJ4e (ORCPT ); Tue, 23 Oct 2007 05:56:34 -0400 Date: Tue, 23 Oct 2007 11:55:07 +0200 From: Jens Axboe To: Boaz Harrosh Cc: Linus Torvalds , Alan Cox , Geert Uytterhoeven , Linux Kernel Development , mingo@elte.hu, Linux/m68k Subject: Re: [PATCH 09/10] Change table chaining layout Message-ID: <20071023095507.GE5059@kernel.dk> References: <1193076664-13652-10-git-send-email-jens.axboe@oracle.com> <20071022211617.31f5c63d@the-village.bc.nu> <20071022224343.4abf3c96@the-village.bc.nu> <471DBEF4.4030303@panasas.com> <20071023094142.GD5059@kernel.dk> <471DC3D9.2070809@panasas.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <471DC3D9.2070809@panasas.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3012 Lines: 60 On Tue, Oct 23 2007, Boaz Harrosh wrote: > On Tue, Oct 23 2007 at 11:41 +0200, Jens Axboe wrote: > > On Tue, Oct 23 2007, Boaz Harrosh wrote: > >> On Mon, Oct 22 2007 at 23:47 +0200, Linus Torvalds wrote: > >>> On Mon, 22 Oct 2007, Alan Cox wrote: > >>> > >>>> For structures, not array elements or stack objects. Does gcc now get > >>>> aligned correct as an attribute on a stack object ? > >>> I think m68k stack layout still guarantees 4-byte-alignment, no? > >>> > >>>> Still doesn't answer the rather more important question - why not just > >>>> stick a NULL on the end instead of all the nutty hacks ? > >>> You still do need one bit for the discontiguous case, so it's not like you > >>> can avoid the hacks anyway (unless you just blow up the structure > >>> entirely) and make it a separate member). So once you have that > >>> bit+pointer, using a separate NULL entry isn't exactly prettier. > >>> > >>> Especially as we actally want to see the difference between > >>> "end-of-allocation" and "not yet filled in", so you shouldn't use NULL > >>> anyway, you should probably use something like "all-ones". > >>> > >>> Linus > >>> - > >> Every one is so hysterical about this sg-chaining problem. And massive > >> patches produced, that when a simple none intrusive solution is proposed > >> it is totally ignored because every one thinks, "I can not be that stupid". > >> Well Einstein said: "Simplicity is the ultimate sophistication". So no one > >> need to feel bad. > > > > It's all about the end goal - having maintainable and resilient code. > > And I think the sg code will be better once we get past the next day or > > so, and it'll be more robust. That is what matters to me, not the > > simplicity of the patch itself. > > > > But that is exactly what his patch is. Much more robust. Because you do not > relay on sglist content but on outside information, that you already have. > Have you had an hard look at his solution? It just simply falls into place. > Please try it out for yourself. I did, and it works. Sure, I looked at it, it's not exactly rocket science, I do understand what it achieves. I don't think the patch is bad as such, I'm merely trying to state that I think the end code AND interface will be much nicer with the current direction that the sg helpers are moving. It does rely on outside context, because you need to pass in the sglist number. In my opinion, this patch would be a bandaid for the original chain code until we got around to fixing the PAGEALLOC crash. Which we did, it's now merged. The patch doesn't make the code cleaner, it makes it uglier. It'll work, but that still doesn't mean I have to agree it's a nice design. -- Jens Axboe - 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/