Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759302AbZDXIlF (ORCPT ); Fri, 24 Apr 2009 04:41:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759087AbZDXIkv (ORCPT ); Fri, 24 Apr 2009 04:40:51 -0400 Received: from mga01.intel.com ([192.55.52.88]:3662 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759336AbZDXIks convert rfc822-to-8bit (ORCPT ); Fri, 24 Apr 2009 04:40:48 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.40,240,1239001200"; d="scan'208";a="684582922" From: "Metzger, Markus T" To: Ingo Molnar , Andrew Morton , "a.p.zijlstra@chello.nl" CC: "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" Date: Fri, 24 Apr 2009 09:39:38 +0100 Subject: RE: [rfc 2/2] x86, bts: use physically non-contiguous trace buffer Thread-Topic: [rfc 2/2] x86, bts: use physically non-contiguous trace buffer Thread-Index: AcnEtxmvI5JbLj3VTOC8+hMAYB53XgAAC6FQ Message-ID: <928CFBE8E7CB0040959E56B4EA41A77E9BA9BB93@irsmsx504.ger.corp.intel.com> References: <20090424100055.A30408@sedona.ch.intel.com> <20090424011328.b5e949ce.akpm@linux-foundation.org> <20090424083128.GI24912@elte.hu> In-Reply-To: <20090424083128.GI24912@elte.hu> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3766 Lines: 101 >-----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. The original suggestion was to use the page allocator and vmap(). I assume you don't want that, either. thanks, markus. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. -- 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/