Re: [RESEND Patch] kcore: remove its pointless size

Andrew Morton
2009-07-17T22:30:33Z

On Thu, 2 Jul 2009 09:41:38 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> On Wed, 1 Jul 2009 17:12:49 -0700
> Andrew Morton <akpm@linux-foundation.org> wrote:
>
> > On Wed, 01 Jul 2009 16:25:05 -0700 ebiederm@xmission.com (Eric W. Biederman) wrote:
> > > Which is better than showing a random number of dubious relationship
> > > to the size we normally show. That code is just a maintenance problem.
> >
> > Well it's not just that st_size is wrong before the first read. It's
> > also wrong after memory hot-add, up until the next read.
> >
> And I found kclist_add() is not called at memory hotplug...
>
>
> > > > If so, should we run get_kcore_size() in proc_kcore_init(), perhaps?
> > > >
> > > > In fact, do we need to run get_kcore_size() more than once per boot?
> > > >
> > > > AFAICT we only run kclist_add() during bootup, so if proc_kcore_init()
> > > > is called at the appropriate time, we can permanently cache its result?
> > > >
> > > > In which case get_kcore_size() and kclist_add() can be marked __init.
> > > >
> > > > Maybe that's all wrong - I didn't look terribly closely.
> > >
> > > Memory hot add I expect is the excuse. There is more that could be
> > > done. But this patch is an obvious bit of chipping away nonsense
> > > code.
> >
> > We have the infrastructure to get this right, I think:
> >
> > - run
> >
> > proc_root_kcore->size = get_kcore_size(...)
> >
> > within proc_kcore_init()
> >
> yes, seems sane.
>
>
> > - register a memory-hotplug notifier and each time memory goes online
> > or offline, rerun
> >
> > proc_root_kcore->size = get_kcore_size(...)
> >
> yes. and we need kclist_add() under memory hotplug.
>
>
> > - stop running get_kcore_size() within read_kcore().
> >
> > I suspect that read_kcore() will not behave well if a memory hotplug
> > operation happens concurrently. But that's a separate problem.
> >
> > (hopefully cc's some memory-hotplug people)
> >
> Maybe no problem. I don't think people does memory hotplug while he reads
> /proc/kcore. (It sounds like modify coredump while investigating it.)
>

I think I'm about to forget about the above issues. If everyone else
does the same, they won't get addressed. Oh well.

And I still need to decide whether
kcore-fix-proc-kcores-statst_size.patch fixes things up sufficiently
well to justify merging it.