Re: [RFC] __GFP_UNMAPPED and __GFP_PRIVATE follow up

["David Hildenbrand (Arm)" <david@kernel.org>]

On 5/15/26 11:43, Brendan Jackman wrote:
> On Thu May 14, 2026 at 5:42 PM UTC, Gregory Price wrote:
> ...
>> Maybe we could modify alloc_flags to be a struct, and export that
>> without being tied to down to a 32/64-bit flag field - and mark certain
>> sets of alloc flags verboten (internally controlled / controlled by GFP
>> flags, and will either be ignored or cause a BUG()).
>>
>> Then we could get something like:
>>
>>     struct alloc_flags {
>>         /* 
>> 	 * internal only: will be ignored, cleared, or cause BUG() if used,
>> 	 * or should be applied via the appropriate __GFP flag.
>> 	 */
>>         uint64_t wmark_min : 1;
>>         uint64_t wmark_low : 1;
>>         uint64_t wmark_high : 1;
>> 	... etc ...
>> 	/* 
>> 	 * external context flags
>> 	 * allows explicit access to certain resources
>> 	 */
>> 	uint64_t cma          : 1; /* allows access to CMA regions */
>> 	uint64_t unmapped     : 1; /* return pages in unmapped state */
>> 	uint64_t managed_node : 1; /* allows access to managed node */
>> 	... etc ...
>>     };

Wouldn't it be cleaner to really only export what we want external users to
consume? IOW, a split between internal and external flags. We do that for
gup-flags, but I wouldn't suggest that models as is, just the overall idea.
There are other ways to achieve it I guess.

-- 
Cheers,

David