Re: [PATCH v2 3/4] mm: hugetlb: fix GFP mask propagation to CMA

[Qi Zheng <qi.zheng@linux.dev>]

Hi Oscar,

On 11/5/26 6:00 PM, Oscar Salvador (SUSE) wrote:
> On Thu, Nov 05, 2026 at 12:07:45PM +0800, Qi Zheng wrote:
>> From: Qi Zheng <zhengqi.arch@bytedance.com>
>>
>> cma_alloc_frozen_compound() uses GFP_KERNEL, allowing direct reclaim
>> during the first MPOL_PREFERRED_MANY allocation attempt even though
>> the caller clears __GFP_DIRECT_RECLAIM.
>>
>> Pass the caller's GFP mask through the helper so CMA respects its
>> reclaim constraints when trying the preferred nodes.
>>
>> Fixes: 9bda131c6093 ("mm: cma: add cma_alloc_frozen{_compound}()")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ...
>> --- a/mm/cma.c
>> +++ b/mm/cma.c
>> @@ -933,9 +933,9 @@ struct page *cma_alloc_frozen(struct cma *cma, unsigned long count,
>>   	return __cma_alloc_frozen(cma, count, align, gfp);
>>   }
>>   
>> -struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order)
>> +struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order, gfp_t gfp)
>>   {
>> -	gfp_t gfp = GFP_KERNEL | __GFP_COMP | __GFP_NOWARN;
>> +	gfp |= __GFP_COMP | __GFP_NOWARN;
> 
> Do we really need __GFP_COMP | __GFP_NOWARN here?
> It is my understanding that all allocations coming from hugetlb are
> handled with htlb_alloc_mask(), and that should already provide
> __GFP_COMP | __GFP_NOWARN.

Right. All current callers already supply both flags through
htlb_alloc_mask().

> We might have needed it when cma_alloc_frozen_compound() constructed its
> own mask, but not it gets it from the caller, and that should have been
> done via htlb_alloc_mask() up the chain.

Right. Now that we restore GFP propagation, setting __GFP_NOWARN here is
redundant. I'll remove it.

I'd still prefer to keep __GFP_COMP so that
cma_alloc_frozen_compound() itself guarantees compound allocation,
without requiring callers to supply the flag.

What do you think?

Thanks,
Qi

> 
> So, any reason to have it here now?
> 
>   
>