linux-kernel - Re: [PATCH] perf: do not flush maps on COMM for perf report

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Date:	Wed, 22 Aug 2012 12:42:22 -0600
From:	David Ahern <dsahern@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	Luigi Semenzato <semenzato@...omium.org>,
	Ingo Molnar <mingo@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Stephen Wilson <wilsons@...rt.ca>,
	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...il.com>,
	Robert Richter <robert.richter@....com>,
	linux-kernel@...r.kernel.org, sonnyrao@...omium.org,
	olofj@...omium.org, eranian@...gle.com
Subject: Re: [PATCH] perf: do not flush maps on COMM for perf report

On 8/22/12 12:16 PM, Arnaldo Carvalho de Melo wrote:
> Em Wed, Aug 22, 2012 at 10:56:13AM -0600, David Ahern escreveu:
>> On 8/22/12 10:29 AM, Arnaldo Carvalho de Melo wrote:
>>> Adding the EXEC event, ditto. And I agree that while adding it we want
>>> to do 1/2 as pre-requisite.
>>
>> maps should not be flushed on a COMM event, so that was a mistake.
>> Given that what new information does an EXEC event provide? Same
>> process id. A COMM event is generated on an exec, so the name change
>> happens. Mappings are dropped prior to that - and there is no unmap
>> event. That seems to be a missing piece. Maps are added which is
>> handled by MMAP events. After that why is an exec event relevant?
>
> Please read the original discussion about it:
>
> https://lkml.org/lkml/2012/2/13/545

I do recall that discussion (and re-read just now). If maps are not 
flushed on a rename (and they should not be), then I still do not 
understand what information is conveyed by an exec event? It's not a new 
process or new map and the name change is already handled by a comm event.

David

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