Re: [PATCH 1/3] mm: move internal mempolicy APIs to new internal header

[Gregory Price]

On Thu, Jul 16, 2026 at 04:57:37PM +0000, Brendan Jackman wrote:
> On Thu Jul 16, 2026 at 4:48 PM UTC, Matthew Wilcox wrote:
> > On Thu, Jul 16, 2026 at 02:30:10PM +0000, Brendan Jackman wrote:
> >> There are no external users for this surface, reduce the scope.
> >> -struct folio *folio_alloc_mpol_noprof(gfp_t gfp, unsigned int order,
> >> -		struct mempolicy *mpol, pgoff_t ilx, int nid);
> >
> > Hm.  So what we're saying is that allocations which respect mempolicy are
> > only for core mm and not for, eg, device drivers to do.  Is that really
> > what we want to say?  I don't think so, because that's inconsistent
> > with having just widened __filemap_get_folio_mpol to allow guest_memfd
> > to specify a mempolicy.
> 
> Yeah I agree, mempolicy definitely seems like a "public concept".  All
> I'm saying here is this specific function doesn't have any external
> users so it doesn't need to be an external header. 
> 
> ... With the ulterior motive that I want to add a new parameter to it
> that actually _is_ mm-internal. Namely, alloc_flags, so I can add
> ALLOC_UNMAPPED to implement AS_NO_DIRECT_MAP, i.e. the next iteration of
> [0]. So basically this is
> about trying to extend the allocator without creating a GFP flag.
> 
> So I'm envisaging if an external user arises for it later, we'd slap two
> underscores on the beginning of the internal one, (with the alloc_flags
> arg), and then bring back the public one as a wrapper.
> 
> Does that make sense?
> 
> [0]: https://lore.kernel.org/all/20260410151746.61150-1-kalyazin@xxxxxxxxxx/
> 

fwiw i've been fiddling with a module side mempolicy interface for a bit
to allow a clean guest_memfd() + mempolicy() interaction [0][1].

I saw this and thought "maybe, maybe not entirely".

there is definitely some oddities in the mempolicy uapi (internal-only
flags that are exposed to the uapi is odd) that some of the interface is
worth internalizing.

(fyi i've converted my private node work on top of the alloc_flags
 addition + new zonelists, new rfc is being posted today, your recent
 merges were timely).

~Gregory

[0] https://github.com/gourryinverse/linux/commit/b25bb27602fe512733450a97ac31ef4387b7e727
[1] https://github.com/gourryinverse/linux/commit/670f7dd81ef33a9385985a54b8ad6bc070b2d581