Messages in this thread | | | Date | Thu, 2 Jul 2009 09:41:38 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [RESEND Patch] kcore: remove its pointless size |
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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.)
Thanks, -Kame
> > Or we just leave /proc/kcore's st_size at zero. It's a pretty hopeless > exercise trying to get this "right", as nobody can safely _use_ that > size - it can be wrong as soon as the caller has read from it. > >
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