Re: [PATCH 1/2] mm: NUMA stats code cleanup and enhancement

[Michal Hocko <mhocko@kernel.org>]

On Thu 14-12-17 16:55:54, kemi wrote:
> 
> 
> On 2017a1'12ae??14ae?JPY 15:29, Michal Hocko wrote:
> > On Thu 14-12-17 09:40:32, kemi wrote:
> >>
> >>
> >> or sometimes 
> >> NUMA stats can't be disabled in their environments.
> > 
> > why?
> > 
> >> That's the reason
> >> why we spent time to do that optimization other than simply adding a runtime
> >> configuration interface.
> >>
> >> Furthermore, the code we optimized for is the core area of kernel that can
> >> benefit most of kernel actions, more or less I think.
> >>
> >> All right, let's think about it in another way, does a u64 percpu array per-node
> >> for NUMA stats really make code too much complicated and hard to maintain?
> >> I'm afraid not IMHO.
> > 
> > I disagree. The whole numa stat things has turned out to be nasty to
> > maintain. For a very limited gain. Now you are just shifting that
> > elsewhere. Look, there are other counters taken in the allocator, we do
> > not want to treat them specially. We have a nice per-cpu infrastructure
> > here so I really fail to see why we should code-around it. If that can
> > be improved then by all means let's do it.
> > 
> 
> Yes, I agree with you that we may improve current per-cpu infrastructure.
> May we have a chance to increase the size of vm_node_stat_diff from s8 to s16 for
> this "per-cpu infrastructure" (s32 in per-cpu counter infrastructure)? The 
> limitation of type s8 seems not enough with more and more cpu cores, especially
> for those monotone increasing type of counters like NUMA counters.
> 
>                                before     after(moving numa to per_cpu_nodestat
>                                               and change s8 to s16)   
> sizeof(struct per_cpu_nodestat)  28                 68
> 
> If ok, we can also keep that improvement in a nice way.

I wouldn't be opposed. Maybe we should make it nr_cpus sized.

-- 
Michal Hocko
SUSE Labs

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