Messages in this thread | | | Date | Thu, 12 Jan 2012 17:13:32 +0200 | Subject | Re: [PATCH 2/2] mm: page allocator: Do not drain per-cpu lists via IPI from page allocator context | From | Gilad Ben-Yossef <> |
| |
On Thu, Jan 12, 2012 at 5:08 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > On Thu, 2012-01-12 at 16:51 +0200, Gilad Ben-Yossef wrote: >> What I can't figure out is why we don't need get/put_online_cpus() >> pair around each and every call >> to on_each_cpu everywhere? and if we do, perhaps making it a part of >> on_each_cpu is the way to go? >> >> Something like: >> >> diff --git a/kernel/smp.c b/kernel/smp.c >> index f66a1b2..cfa3882 100644 >> --- a/kernel/smp.c >> +++ b/kernel/smp.c >> @@ -691,11 +691,15 @@ void on_each_cpu(void (*func) (void *info), void >> *info, int wait) >> { >> unsigned long flags; >> >> + BUG_ON(in_atomic()); >> + >> + get_online_cpus(); >> preempt_disable(); > > Your preempt_disable() here serializes against hotplug..
I'm probably daft, but why didn't it work for the page allocator then?
Mel's description reads: "Part of the problem is the page allocator is sending IPIs using on_each_cpu() without calling get_online_cpus() to prevent changes to the online cpumask."
on_each_cpu() disables preemption in master as well...
Gilad
Thanks, Gilad
-- Gilad Ben-Yossef Chief Coffee Drinker gilad@benyossef.com Israel Cell: +972-52-8260388 US Cell: +1-973-8260388 http://benyossef.com
"Unfortunately, cache misses are an equal opportunity pain provider." -- Mike Galbraith, LKML -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |