Re: [RFC PATCH 1/4] mm: migrate: Allow misplaced migration without VMA too

[Gregory Price]

On Thu, Mar 06, 2025 at 06:42:10PM +0000, Matthew Wilcox wrote:
> On Thu, Mar 06, 2025 at 01:19:41PM -0500, Gregory Price wrote:
> > Divorced from the tiering mechanisms, is making misplaced migration able
> > to migrate unmapped pages not generally useful?
> 
> The only thing I can think of is if you have a process or set of
> processes on node A calling read() and the file is cached on node B.
> But in order to decide if the page is on the wrong node, you'd need
> to track a lot of information about which nodes the page is being
> accessed from.  Which is probably why we've never bothered to do it.
> 
> This is not a large patch for you to carry as part of your patchset.
> There's nothing intrinsically wrong with it; it just has no users in
> mainline and no real prospect of any being added soon.

That's fair, I'm just tracking 3-4 different RFCs that are going to butt
up against this, so wanted to assess whether getting the patches out
ahead would save some strife.

~Gregory