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

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Date:	Tue, 15 Jan 2008 10:03:16 +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:
> 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.

> 
> 
> BTW, have you ever tested this patch? If you don't have any test environment
> for memory hotplug code, then I'll check it. :-)

Well, I tested it but not in "real configuration": what I did is that I 
changed the status by hand under sysfs to offline. I also changed 
remove_memory() in mm/memory_hotplug.c in the following way (instead of 
returninf EINVAL):
1) decrease the total_ram pages
2) call memory_notify(MEM_OFFLINE, NULL)

and checked that the msgmni was recomputed.

But sure, if you are candidate to test it, that would be great!

Regards,
Nadia

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