linux-kernel - Re: [RFC][PATCH] /proc/pid/maps doesn't match "ipcs -m" shmid

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Date:	Thu, 7 Jun 2007 00:53:19 -0400
From:	"Albert Cahalan" <acahalan@...il.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	ebiederm@...ssion.com, pbadari@...ibm.com,
	torvalds@...ux-foundation.org
Subject: Re: [RFC][PATCH] /proc/pid/maps doesn't match "ipcs -m" shmid

On 6/6/07, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Wed, 6 Jun 2007 23:27:01 -0400 "Albert Cahalan" <acahalan@...il.com> wrote:
> > Eric W. Biederman writes:
> > > Badari Pulavarty <pbadari@...ibm.com> writes:
> >
> > >> Your recent cleanup to shm code, namely
> > >>
> > >> [PATCH] shm: make sysv ipc shared memory use stacked files
> > >>
> > >> took away one of the debugging feature for shm segments.
> > >> Originally, shmid were forced to be the inode numbers and
> > >> they show up in /proc/pid/maps for the process which mapped
> > >> this shared memory segments (vma listing). That way, its easy
> > >> to find out who all mapped this shared memory segment. Your
> > >> patchset, took away the inode# setting. So, we can't easily
> > >> match the shmem segments to /proc/pid/maps easily. (It was
> > >> really useful in tracking down a customer problem recently).
> > >> Is this done deliberately ? Anything wrong in setting this back ?
> > >
> > > Theoretically it makes the stacked file concept more brittle,
> > > because it means the lower layers can't care about their inode
> > > number.
> > >
> > > We do need something to tie these things together.
> > >
> > > So I suspect what makes most sense is to simply rename the
> > > dentry SYSVID<segmentid>
> >
> > Please stop breaking things in /proc. The pmap command relys
> > on the old behavior.
>
> What effect did this change have upon the pmap command?  Details, please.
>
> > It's time to revert.
>
> Probably true, but we'd need to understand what the impact was.

Very simply, pmap reports the shmid.

albert 0 ~$ pmap `pidof X` | egrep -2 shmid
30050000  16384K rw-s-  /dev/fb0
31050000    152K rw---    [ anon ]
31076000    384K rw-s-    [ shmid=0x3f428000 ]
310d6000    384K rw-s-    [ shmid=0x3f430001 ]
31136000    384K rw-s-    [ shmid=0x3f438002 ]
31196000    384K rw-s-    [ shmid=0x3f440003 ]
311f6000    384K rw-s-    [ shmid=0x3f448004 ]
31256000    384K rw-s-    [ shmid=0x3f450005 ]
312b6000    384K rw-s-    [ shmid=0x3f460006 ]
31316000    384K rw-s-    [ shmid=0x3f870007 ]
31491000    140K r----  /usr/share/fonts/type1/gsfonts/n021003l.pfb
3150e000   9496K rw---    [ anon ]
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