per-cpu counters presently must iterate over all possible CPUs in the
exhaustive percpu_counter_sum().
But it can be much better to only iterate over the presently-online CPUs. To
do this, we must arrange for an offlined CPU's count to be spilled into the
counter's central count.
We can do this for all percpu_counters in the machine by linking them into a
single global list and walking that list at CPU_DEAD time.
(I hope. Might have race windows in which the percpu_counter_sum() count is
inaccurate?)
Cc: Gautham R Shenoy <ego@in.ibm.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
c67ad917cb