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

Albert Cahalan
2007-06-07T04:53:20Z

On 6/6/07, Andrew Morton <akpm@linux-foundation.org> wrote:
> On Wed, 6 Jun 2007 23:27:01 -0400 "Albert Cahalan" <acahalan@gmail.com> wrote:
> > Eric W. Biederman writes:
> > > Badari Pulavarty <pbadari@us.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 ]