Re: [PATCH 0/6 v2] Calculate pcp->high based on zone sizes and active CPUs

David Hildenbrand
2021-05-28T09:03:30Z

On 28.05.21 10:55, Mel Gorman wrote:
> On Thu, May 27, 2021 at 12:36:21PM -0700, Dave Hansen wrote:
>> Hi Mel,
>>
>> Feng Tang tossed these on a "Cascade Lake" system with 96 threads and
>> ~512G of persistent memory and 128G of DRAM. The PMEM is in "volatile
>> use" mode and being managed via the buddy just like the normal RAM.
>>
>> The PMEM zones are big ones:
>>
>> present 65011712 = 248 G
>> high 134595 = 525 M
>>
>> The PMEM nodes, of course, don't have any CPUs in them.
>>
>> With your series, the pcp->high value per-cpu is 69584 pages or about
>> 270MB per CPU. Scaled up by the 96 CPU threads, that's ~26GB of
>> worst-case memory in the pcps per zone, or roughly 10% of the size of
>> the zone.

When I read about having such big amounts of free memory theoretically
stuck in PCP lists, I guess we really want to start draining the PCP in
alloc_contig_range(), just as we do with memory hotunplug when offlining.

--
Thanks,

David / dhildenb