Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932172AbWCIQJ2 (ORCPT ); Thu, 9 Mar 2006 11:09:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751836AbWCIQJ2 (ORCPT ); Thu, 9 Mar 2006 11:09:28 -0500 Received: from smtp.osdl.org ([65.172.181.4]:18359 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S1751269AbWCIQJ1 (ORCPT ); Thu, 9 Mar 2006 11:09:27 -0500 Date: Thu, 9 Mar 2006 08:08:52 -0800 (PST) From: Linus Torvalds To: "Martin J. Bligh" cc: Dave Jones , Jesper Juhl , Jens Axboe , Linux Kernel Mailing List , Andrew Morton , markhe@nextd.demon.co.uk, Andrea Arcangeli , Mike Christie , James Bottomley Subject: Re: Slab corruption in 2.6.16-rc5-mm2 In-Reply-To: <44104EB7.9090103@mbligh.org> Message-ID: References: <200603060117.16484.jesper.juhl@gmail.com> <200603062124.42223.jesper.juhl@gmail.com> <20060306203036.GQ4595@suse.de> <9a8748490603061341l50febef9o3cb480bdbdcf925f@mail.gmail.com> <20060306215515.GE11565@redhat.com> <44104EB7.9090103@mbligh.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1617 Lines: 39 On Thu, 9 Mar 2006, Martin J. Bligh wrote: > > > > DEBUG_PAGEALLOC in particular is *fantastic* at making bugs hide. > > I've lost many an hour trying to pin bugs down due to that. > > Is this backwards? We're saying DEBUG_PAGEALLOC is bad? DEBUG_PAGEALLOC is great for finding the really stupid kinds of bugs, and it's definitely worth doing every once in a while. However, DEBUG_PAGEALLOC makes many things orders of magnitude slower, and it eats memory like mad (because it turns some slabs into whole pages - but it still doesn't help small allocation debugging that much). So unlike DEBUG_SLAB, it's not reasonable to have it on all the time. IOW, DEBUG_SLAB is something that a distro kernel can reasonably enable for users by default (I think fedora-devel does, for example). In contrast, DEBUG_PAGEALLOC is more of a "useful for special cases" thing, where you want to validate that there's nothing _obviously_ bad going on. > Do we NOT want to have DEBUG_SLAB and DEBUG_PAGEALLOC both enabled? I suspect that once DEBUG_PAGEALLOC is on, whether you do DEBUG_SLAB or not is a toss-up. The interesting cases tend to be - neither: usable for benchmarking - DEBUG_SLAB: perfectly usable for normal work - DEBUG_PAGEALLOC (with or without DEBUG_SLAB): debugging tool only At least that's my opinion, maybe others have other experiences. Linus - 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/