Hello,
On Thu, Jun 25, 2015 at 09:08:00PM +0200, Peter Zijlstra wrote:
> > mm/memcontrol.c:mem_cgroup_read_events
> > mm/memcontrol.c:mem_cgroup_read_stat
>
> Those seem to be hotplug challenged. I'm thinking dropping that
> nocpu_base.count[] crap and just iterating all possible CPUs would've
> been much easier.
A patch doing that is already queued for this merge window. IIRC,
it's included as part of cgroup writeback updates.
> > > +#define per_cpu_sum(var) \
> > > +({ \
> > > + typeof(var) __sum = 0; \
> > > + int cpu; \
> > > + for_each_possible_cpu(cpu) \
> > > + __sum += per_cpu(var, cpu); \
> > > + __sum; \
> > > +})
> > > +
> >
> > so maybe put it into include/linux/percpu.h ?
percpu-defs.h would be the better place for it.
> Yes I can do that.
>
> We can try and use it more after that, there seems to be loads of places
> that could use this fs/namespace.c fs/inode.c etc..
Hmmm... the only worry I have about this is people using it on u64 on
32bit machines. CPU local ops can do split updates on lower and upper
halves and the remotely-read value will be surprising. We have the
same issues w/ regular per_cpu accesses to but the summing function /
macro is better at giving the false sense of security. Prolly
limiting it upto ulong size is a good idea?
Thanks.
--
tejun
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