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

[Gregory Price <gourry@gourry.net>]

On Mon, Jul 20, 2026 at 06:52:02PM +0100, Matthew Wilcox wrote:
> 
> > ... 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.
> 
> Yeah.  I'm not sold on the whole alloc_flags thing, but I'm too busy to
> sit down and think it through properly to get involved in a proper
> argument about how it should work.
> 
> My entirely unresearched and ill-considered opinion is that the __GFP
> flags should _be_ the ALLOC flags.  We shoudn't be translating GFP flags
> into ALLOC flags that are what the allocator actually uses, the
> translation should be done at compile time.  So if GFP_KERNEL and
> GFP_ATOMIC need to be composed of different flags with different
> semantics, then we should do that, not invent a different set of flags
> that special people can use for special purposes.
> 

alloc_flags is putting me between a rock and a hard place.

I figured out a clean isolation mechanism with zonelists (new rfc is
posting today, i'm doing one last proofread), but it required me to
extend some of the mm/ internal interfaces with a zonelist selector.

Since Brendan's base work made it in mm-new, i decided to replace
the zonelist selector with ALLOC_ZONELIST_PRIVATE as the selector
to avoid *yet more* arguments.

I'll be posting with ALLOC_ZONELIST_PRIVATE on top of mm-new, but
the churn is getting painful.

It really seems like we just want an mm/ internal interface that
exposes struct alloc_context for specific *mm/* callers
(see: compaction_context, migration_context, etc), and interfaces
that keep this nonsense transparent for everyone else.

Then if you want access to alloc_context interface, you need to get
export approval for that component (similar to EXPORT_FOR_MODULES).

Just spitballing here, but the churn is killing me.

~Gregory