On 2019/9/17 18:08, Michal Hocko wrote: > On Tue 17-09-19 17:53:57, Yunsheng Lin wrote: >> On 2019/9/17 17:36, Michal Hocko wrote: >>> On Tue 17-09-19 14:20:11, Yunsheng Lin wrote: >>>> On 2019/9/17 13:28, Michael Ellerman wrote: >>>>> Yunsheng Lin <linyunsheng@xxxxxxxxxx> writes: >>> [...] >>>>>> But we cannot really copy the page allocator logic. Simply because the >>>>>> page allocator doesn't enforce the near node affinity. It just picks it >>>>>> up as a preferred node but then it is free to fallback to any other numa >>>>>> node. This is not the case here and node_to_cpumask_map will only restrict >>>>>> to the particular node's cpus which would have really non deterministic >>>>>> behavior depending on where the code is executed. So in fact we really >>>>>> want to return cpu_online_mask for NUMA_NO_NODE. >>>>>> >>>>>> Some arches were already NUMA_NO_NODE aware, but they return cpu_all_mask, >>>>>> which should be identical with cpu_online_mask when those arches do not >>>>>> support cpu hotplug, this patch also changes them to return cpu_online_mask >>>>>> in order to be consistent and use NUMA_NO_NODE instead of "-1". >>>>> >>>>> Except some of those arches *do* support CPU hotplug, powerpc and sparc >>>>> at least. So switching from cpu_all_mask to cpu_online_mask is a >>>>> meaningful change. >>>> >>>> Yes, thanks for pointing out. >>>> >>>>> >>>>> That doesn't mean it's wrong, but you need to explain why it's the right >>>>> change. >>>> >>>> How about adding the below to the commit log: >>>> Even if some of the arches do support CPU hotplug, it does not make sense >>>> to return the cpu that has been hotplugged. >>>> >>>> Any suggestion? >>> >>> Again, for the third time, I believe. Make it a separate patch please. >>> There is absolutely no reason to conflate those two things. >> >> Ok, thanks. >> Will make the cpu_all_mask -> cpu_online_mask change a separate patch. > > Thanks. This really needs per arch maintainer to check closely. > >> Also, do you think it is better to resend this as individual patches for each arch >> or have all these changes in a single patch? I am not sure which is the common >> practice for a multi-arches changes like this. > > It really depends on arch maintainers. Both approaches have some pros > and cons. A single patch is more compact and and parts are not going to > get lost in noise. They might generate some conflicts with parallel > changes. I suspect a conflict risk is quite low in this code considering > from a recent activity. A follow up arch specific patch would have to be > routed via Andrew as well. > > If Andrew is ok routing it through his tree and none of the arch > maintainers is opposed then I would go with a single patch. Ok, I will try a single patch for NUMA_NO_NODE aware change first. "cpu_all_mask -> cpu_online_mask" change seems a little controversial, and may need deeper investigation. >
