I am trying to optimize the memory footprint of some code of mine.
It's been using per-cpu data and alloc_percpu() so far. The latter has
the disadvantage of getting hold of memory for CPU's which aren't there
(yet).
I could imagine using CPU-hotplug notifications as triggers for
additional allocations or for cleaning up unneeded memory. But
alloc_percpu() appears to conflict with that idea.
I was briefly tempted to derive some code from alloc_percpu() more to my
liking, until I was scared off by this comment in alloc_percpu():
/*
* Cannot use for_each_online_cpu since a cpu may come online
* and we have no way of figuring out how to fix the array
* that we have allocated then....
*/
Well, and then there is kernel/profile.c, for example, which boldly
ignors alloc_percpu()'s qualms and allocates and releases per-cpu data
as needed.
Is that the way to go?
If so, why alloc_percpu()'s reservations?
Or, does that comment imply that the exploiter isn't expected to take
care of CPU hotplug events?
Am I missing anything?
Thank you.
Martin