Re: [PATCH v3 05/16] mm/page_alloc: unify __alloc_frozen_pages[_nolock]_noprof()

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

On 6/30/26 15:36, Harry Yoo wrote:
> 
> 
> On 6/29/26 10:11 PM, Brendan Jackman wrote:
>> Currently the core allocator code is controlled by ALLOC_NOLOCK, but the
>> main entry point function is significantly different from the normal
>> __alloc_frozen_pages_nolock(), this is tiring when reading the code.
>> 
>> Plumb the ALLOC_NOLOCK control one layer up in the call stack: create
>> an alloc_flags argument to __alloc_frozen_pages_nolock() (which is only
>> exposed to mm/) and then turn the nolock variant into a thin wrapper
>> that just sets that flag (as well as handling NUMA_NO_NODE, similar to
>> how some of the wrappers in gfp.h do).
>> 
>> Rationale that this doesn't change anything:
>>
>> 1. Simple bits: A bunch of the nolock-specific handling is just moved to
>>    the new alloc_order_allowed(), alloc_trylock_allowed() and
>>    gfp_trylock.
> 
> Right.
> 
>> 2. __alloc_frozen_pages_noprof() has some extra logic that wasn't
>>    previously in the nolock variant:
>> 
>>    a. Application of gfp_allowed_mask; this only affects early boot, and
>>       only flags that affect the slowpath get changed here.
> 
> gfp_allowed_mask clears __GFP_RECLAIM, and that means now allocations
> with GFP_KERNEL during early boot would see
> gfpflags_allow_spinning() = false.

Is it a problem though? non-nolock allocations were affected before (the
masking existed for those already) and will be affected now the same, and
_nolock() allocations don't pass __GFP_RECLAIM in the first place, so the
masking can't affect them?

> The helper is not used in in the page allocator, but used in
> memcg/stackdepot/page_owner.
> 
>>    b. Application of current_gfp_context() - also only affects the
>>       slowpath
> 
> PF_MEMALLOC_PIN affects the fast path, but ALLOC_NOLOCK users
> won't be affected.

And it wouldn't be wrong if they were? It only clears __GFP_MOVABLE?

> What about alloc_flags_nofragment/nonblocking()?

ALLOC_NOFRAGMENT due to e.g. defrag_mode could be a problem indeed, if
there's no slowpath. Make ALLOC_NOLOCK override it?

nonblocking() is probably fine?

>