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

From: Nadia Derbey
Date: Tue Jan 15 2008 - 05:18:56 EST


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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