Re: [RFC PATCH 0/6] mm: pass alloc_flags through folio, filemap, and bulk allocators

[Gregory Price <gourry@gourry.net>]

On Fri, Oct 09, 2026 at 10:55:05PM +0200, David Hildenbrand (Arm) wrote:
> I do agree that two sets of flags is suboptimal, but likely more flexible. I
> guess an alloc_flags only interface is not easily possible ...
> 
> I do wonder whether it should be:
> 
> 	typedef int __bitwise alloc_flags_t;
> 
> instead of "unsigned int alloc_flags".
> 
> ... while at it

Does it make sense to leave alloc_flags to internal-only state
and just implement a new flag field?

gfp_t       -> describe the page (fully public)
req_t       -> describe the allocator behavior (mm-internal only)
alloc_flags -> internal allocator state only

typedef int __bitwise pa_req_t; /* Page Allocator Request Flags */

#define PA_REQ_DEFAULT        0
#define PA_REQ_NOLOCK         BIT(0) /* from ALLOC_NOLOCK */
#define PA_REQ_NO_CODETAG     BIT(1) /* from ALLOC_NO_CODETAG */
#define PA_REQ_SPREAD_DIRTY   BIT(2) /* from __GFP_WRITE */
#define PA_REQ_DEFER_INIT     BIT(3) /* from __GFP_SKIP_ZERO */
#define PA_REQ_ZERO_TAGS      BIT(4) /* from __GFP_ZERO_TAGS */
#define PA_REQ_NO_FALLBACK    BIT(5) /* select no fallback list */
#define PA_REQ_NO_OOM         BIT(6) /* do not oom */

Off the bat we recover 2 ALLOC flags and 3 GFP flags. Possibly more with
a bit more work.

Then we get:

#define PA_REQ_PRIVATE        BIT(7) /* allow private node allocation */
#define PA_REQ_UNMAPPED       BIT(8) /* page must be unmapped */

And we might not even need a new zonelist for private nodes in this case
as long as we require internal users to pass PA_REQ_PRIVATE and add a
function like

folio_alloc_private(void *owner, ...) {
   /* validate (pgdat->owner == owner) before allowing allocation */
   __folio_alloc(..., req | PA_REQ_PRIVATE | PA_REQ_NOFALLBACK, ...);
}

User still has the option to request NO_OOM via __GFP_THISNODE :]

~Gregory