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

[Yang Shi]

On 3/27/19 6:08 AM, Keith Busch wrote:
> 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.

Yes, it still could fail. I can't tell which way is better for now. I 
just thought scanning another round then migrating should be still 
faster than swapping off the top of my head.

Thanks,
Yang