[RFC PATCH 0/4] [RESEND] Change default MSGMNI tunable to scale with lowmem

[Nadia Derbey <Nadia.Derbey@bull.net>]

Hi,

Yesterday, I posted to lkml a series of patches that make the ipc 
tunable msgmni scale with lowmem (see thread 
http://lkml.org/lkml/2008/1/14/196).

Since these patches watch for memory hotplug notifications, I thought 
that comments from linux-mm people would be interesting.

Also, since these patches change the ipc_namespace structure, comments 
from people subscribed at the containers mailing list would be welcome too.

Notes:
1) please, Cc me since I'm not subscribed to linux-mm.
2) sorry for lkml subsribers who are receiving this mail for the 2nd 
time, but I wanted all the comments to be shared.


Here is patch 0, the complete series can be found in the thread 
mentioned above.

-----------------

On large systems we'd like to allow a larger number of message queues. 
In some cases up to 32K. However simply setting MSGMNI to a larger value 
may cause problems for smaller systems.

The first patch of this series introduces a default maximum number of 
message queue ids that scales with the amount of lowmem.

Since msgmni is per namespace and there is no amount of memory dedicated 
to each namespace so far, the second patch of this series scales msgmni 
to the number of ipc namespaces.

In the last patch, a notifier block is added to the ipc namespace 
structure to manage memory hotplug. The callback routine is activated 
upon memory add/remove and it recomputes msgmni. One callback routine is 
added to the memory notifier chain each time an ipc namespace is 
allocated. It is removed when the coresponding ipc namespace is freed.

I still have 1 issue that I'll try to solve next:
   . use the notification mechanism to recompute all the msg_ctlmni each
     time an ipc namespace is created / removed.


These patches should be applied to 2.6.24-rc7, in the following order:

[PATCH 1/4]: ipc_scale_msgmni_with_lowmem.patch
[PATCH 2/4]: ipc_scale_msgmni_with_namespaces.patch
[PATCH 3/4]: ipc_slab_memory_callback_prio_to_const.patch
[PATCH 4/4]: ipc_recompute_msgmni_on_memory_hotplug.patch


Regards,
Nadia

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