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

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Message-ID: <478C881B.5030503@bull.net>
Date:	Tue, 15 Jan 2008 11:16:59 +0100
From:	Nadia Derbey <Nadia.Derbey@...l.net>
To:	Yasunori Goto <y-goto@...fujitsu.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	matthltc@...ibm.com
Subject: Re: [RFC PATCH 4/4] [RESEND] Recomputing msgmni on memory add / remove

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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