Re: [v2 RFC PATCH 0/9] Another Approach to Use PMEM as NUMA Node

[Dave Hansen]

On 4/16/19 8:33 AM, Zi Yan wrote:
>> We have a reasonable argument that demotion is better than
>> swapping. So, we could say that even if a VMA has a strict NUMA
>> policy, demoting pages mapped there pages still beats swapping
>> them or tossing the page cache.  It's doing them a favor to
>> demote them.
> I just wonder whether page migration is always better than
> swapping, since SSD write throughput keeps improving but page
> migration throughput is still low. For example, my machine has a
> SSD with 2GB/s writing throughput but the throughput of 4KB page
> migration is less than 1GB/s, why do we want to use page migration
> for demotion instead of swapping?

Just because we observe that page migration apparently has lower
throughput today doesn't mean that we should consider it a dead end.