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

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Date:	Wed, 14 Aug 2013 12:30:08 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Andi Kleen <ak@...ux.intel.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 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?
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.
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