Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754312AbZDZQJt (ORCPT ); Sun, 26 Apr 2009 12:09:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752755AbZDZQJk (ORCPT ); Sun, 26 Apr 2009 12:09:40 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:38937 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751962AbZDZQJj (ORCPT ); Sun, 26 Apr 2009 12:09:39 -0400 Date: Sun, 26 Apr 2009 18:08:59 +0200 From: Ingo Molnar To: "Metzger, Markus T" Cc: Andrew Morton , "a.p.zijlstra@chello.nl" , "markus.t.metzger@gmail.com" , "roland@redhat.com" , "eranian@googlemail.com" , "oleg@redhat.com" , "Villacis, Juan" , "ak@linux.jf.intel.com" , "linux-kernel@vger.kernel.org" , "tglx@linutronix.de" , "hpa@zytor.com" Subject: Re: [rfc 2/2] x86, bts: use physically non-contiguous trace buffer Message-ID: <20090426160859.GA5420@elte.hu> References: <20090424100055.A30408@sedona.ch.intel.com> <20090424011328.b5e949ce.akpm@linux-foundation.org> <20090424083128.GI24912@elte.hu> <928CFBE8E7CB0040959E56B4EA41A77E9BA9BB93@irsmsx504.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <928CFBE8E7CB0040959E56B4EA41A77E9BA9BB93@irsmsx504.ger.corp.intel.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3488 Lines: 93 * Metzger, Markus T wrote: > >-----Original Message----- > >From: Ingo Molnar [mailto:mingo@elte.hu] > >Sent: Friday, April 24, 2009 10:31 AM > >To: Andrew Morton > >Cc: Metzger, Markus T; a.p.zijlstra@chello.nl; markus.t.metzger@gmail.com; roland@redhat.com; > >eranian@googlemail.com; oleg@redhat.com; Villacis, Juan; ak@linux.jf.intel.com; linux- > >kernel@vger.kernel.org; tglx@linutronix.de; hpa@zytor.com > >Subject: Re: [rfc 2/2] x86, bts: use physically non-contiguous trace buffer > > > > > >* Andrew Morton wrote: > > > >> On Fri, 24 Apr 2009 10:00:55 +0200 Markus Metzger wrote: > >> > >> > Use vmalloc to allocate the branch trace buffer. > >> > > >> > Peter Zijlstra suggested to use vmalloc rather than kmalloc to > >> > allocate the potentially multi-page branch trace buffer. > >> > >> The changelog provides no reason for this change. It should do so. > >> > >> > Is there a way to have vmalloc allocate a physically non-contiguous > >> > buffer for test purposes? Ideally, the memory area would have big > >> > holes in it with sensitive data in between so I would know immediately > >> > when this is overwritten. > >> > >> I suppose you could allocate the pages by hand and then vmap() them. > >> Allocating 2* the number you need and then freeing every second one > >> should make them physically holey. > >> > >> > --- a/arch/x86/kernel/ptrace.c > >> > +++ b/arch/x86/kernel/ptrace.c > >> > @@ -22,6 +22,7 @@ > >> > #include > >> > #include > >> > #include > >> > +#include > >> > > >> > #include > >> > #include > >> > @@ -626,7 +627,7 @@ static int alloc_bts_buffer(struct bts_c > >> > if (err < 0) > >> > return err; > >> > > >> > - buffer = kzalloc(size, GFP_KERNEL); > >> > + buffer = vmalloc(size); > >> > if (!buffer) > >> > goto out_refund; > >> > > >> > @@ -646,7 +647,7 @@ static inline void free_bts_buffer(struc > >> > if (!context->buffer) > >> > return; > >> > > >> > - kfree(context->buffer); > >> > + vfree(context->buffer); > >> > context->buffer = NULL; > >> > > >> > >> The patch looks like a regression to me. vmalloc memory is slower > >> to allocate, slower to free, slower to access and can exhaust or > >> fragment the vmalloc arena. Confused. > > > >Performance does not matter here (this is really a slowpath), but > >fragmentation does matter, especially on 32-bit systems. > > > >I'd not uglify the code via vmap() - and vmap has the same > >fundamental address space limitations on 32-bit as vmalloc(). > > > >The existing kmalloc() is fine. We do larger than PAGE_SIZE > >allocations elsewhere too (the kernel stack for example), and this > >is a debug facility, so failing the allocation is not a big problem > >even if it happens. > > OK. I'll drop 2/2 and send out 1/2 as a patch, then. ok - i've already applied 1/2 so unless you can see a bug we should be fine. > The original suggestion was to use the page allocator and vmap(). > I assume you don't want that, either. Yeah - i'd rather suggest to avoid that complexity - unless there are good reasons. Ingo -- 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/