linux-kernel - Re: [PATCH v1 2/2] perf tools: add attr->mmap2 support

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Message-ID: <20130814164359.GM23412@tassilo.jf.intel.com>
Date:	Wed, 14 Aug 2013 09:43:59 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung.kim@....com>,
	David Ahern <dsahern@...il.com>
Subject: Re: [PATCH v1 2/2] perf tools: add attr->mmap2 support

On Wed, Aug 14, 2013 at 12:30:08PM +0200, Stephane Eranian wrote:
> On Wed, Aug 14, 2013 at 1:34 AM, Andi Kleen <ak@...ux.intel.com> wrote:
> > On Tue, Aug 13, 2013 at 01:55:57PM +0200, Stephane Eranian wrote:
> >> This patch adds support for the new PERF_RECORD_MMAP2
> >> record type exposed by the kernel. This is an extended
> >> PERF_RECORD_MMAP record. It adds for each file-backed
> >> mapping the device major, minor number and the inode
> >> number. This triplet uniquely identifies the source
> >> of a file-backed mapping. It can be used to detect
> >> identical virtual mappings between processes for instance.
> >
> > Can you also add the generation number please?
> > That would make it even more unique.
> >
> I assume you're talkng about inode->i_generation, right?

Yes.

> I could add that one easily. I am surprised to see:
> 
> mm/shmem.c:
> static struct inode *shmem_get_inode(struct super_block *sb, const
> struct inode *dir,
>                                      umode_t mode, dev_t dev, unsigned
> long flags)
> {
>                 inode->i_generation = get_seconds();
> }
> I am assuming that the uniqueness for SHM is coming from the SHMID and therefore
> a poor quality i_generation is sufficient here.

Yes that's odd. But most file system should have a sensible generation
number.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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