Re: [PATCH 06/10] mm: vmscan: demote anon DRAM pages to PMEM node

Keith Busch
2019-03-27T13:07:14Z

On Tue, Mar 26, 2019 at 08:41:15PM -0700, Yang Shi wrote:
> On 3/26/19 5:35 PM, Keith Busch wrote:
> > migration nodes have higher free capacity than source nodes. And since
> > your attempting THP's without ever splitting them, that also requires
> > lower fragmentation for a successful migration.
>
> Yes, it is possible. However, migrate_pages() already has logic to
> handle such case. If the target node has not enough space for migrating
> THP in a whole, it would split THP then retry with base pages.

Oh, you're right, my mistake on splitting. So you have a good best effort
migrate, but I still think it can fail for legitimate reasons that should
have a swap fallback.