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

Nadia Derbey
2008-01-15T10:18:54Z

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