Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755604Ab3I3Qs5 (ORCPT ); Mon, 30 Sep 2013 12:48:57 -0400 Received: from mail-oa0-f49.google.com ([209.85.219.49]:40995 "EHLO mail-oa0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755344Ab3I3Qs4 (ORCPT ); Mon, 30 Sep 2013 12:48:56 -0400 MIME-Version: 1.0 In-Reply-To: <20130930161546.GG3081@twins.programming.kicks-ass.net> References: <20130930161546.GG3081@twins.programming.kicks-ass.net> Date: Mon, 30 Sep 2013 18:48:55 +0200 Message-ID: Subject: Re: [RFC] perf: mmap2 not covering VM_CLONE regions From: Stephane Eranian To: Peter Zijlstra Cc: LKML , "mingo@elte.hu" , "ak@linux.intel.com" , Arnaldo Carvalho de Melo , David Ahern , Jiri Olsa , Hugh Dickins Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1614 Lines: 34 On Mon, Sep 30, 2013 at 6:15 PM, Peter Zijlstra wrote: > On Mon, Sep 30, 2013 at 05:44:41PM +0200, Stephane Eranian wrote: >> Hi, >> >> I was alerted by people trying to use the PERF_RECORD_MMAP2 >> record to disambiguate virtual address mappings that there is a case >> where the record does not contain enough information. >> >> As you know, the MMAP2 record adds the major, minor, ino number, >> inode generation numbers to a mapping. But it does that only for >> file or pseudo -file backed mappings. That covers file mmaps and also >> SYSV shared memory segments. >> >> However there is a another kind of situation that arises in some >> multi-process benchmarks where a region of memory is cloned >> using VM_CLONE. As such, the virtual addresses match between >> the processes but the major, minor, inode, inode generation fields >> are all zeroes because there is no inode associated with the mapping. >> Yet, it is important for the tool to know the mappings between the >> processes are pointing to the same physical data. >> >> We need to cover this case and I am seeking for advice on how to >> best address this need given that we discarded using the plain physical >> address for disambiguation. > > Urgh.. who in his bloody mind is playing VM_CLNOE games that is not > pthread_creatE() ? Some matrix multiply benchmark, I guess. -- 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/