Re: [RFC PATCH 4/4] [RESEND] Recomputing msgmni on memory add / remove

[Nadia Derbey]

Yasunori Goto wrote:
> > Yasunori Goto wrote:
> >
> > > Hello Nadia-san.
> > >
> > >
> > >
> > > > @@ -118,6 +122,10 @@ struct ipc_namespace {
> > > > 	size_t		shm_ctlall;
> > > > 	int		shm_ctlmni;
> > > > 	int		shm_tot;
> > > > +
> > > > +#ifdef CONFIG_MEMORY_HOTPLUG
> > > > +	struct notifier_block ipc_memory_hotplug;
> > > > +#endif
> > > > };
> > >
> > >
> > > I'm sorry, but I don't see why each ipc namespace must have each callbacks
> > > of memory hotplug.
> > > I prefer only one callback for each subsystem, not for each namespace.
> > > In addition, the recompute_msgmni() calculation looks very similar for
> > > all ipc namespace.
> > > Or do you wish each ipc namespace have different callback for the future?
> >
> > Actually, this is what I wanted to do at the very beginning: have a 
> > single callback that would recompute the msgmni for each ipc namespace. 
> > But the issue here is that the namespaces are not linked to each other, 
> > so I had no simple way to go through all the namespaces.
> > I solved the issue by having a callback for any single ipc namespace and 
> > make it recompute the msgmni value for itslef.
>
>
> The recompute_msg() must be called when new ipc_namespace is created/removed
> as you mentioned. I think namespaces should be linked each other for it
> in the end....

Not if I do it the same way as for memory hotplug:
1) definee a "namespace event notifier"
2) insert another notifier block into the ipc namespace.
3) The callback routines in the notifier chain would be activated upon 
namespace creation / removal.

But I'm still thinking about it: Matt Helsley suggested that we might 
just copy the old namespace's value when creating a new namespace.

There's also the issue of an msgmni that has been changed via procfs: 
may be we should not unconditionally recompute it upon namespace 
creation / removal, so unregister the callback for the owning namespace 
as soon as msgmni has been changed from userspace.


Regards,
Nadia
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