Re: [PATCH v4 5/6] mm: cma: add cma_alloc_frozen{_compound}()

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2025/12/17 2:40, Zi Yan wrote:
> On 16 Dec 2025, at 6:48, Kefeng Wang wrote:
> 
>> Introduce cma_alloc_frozen{_compound}() helper to alloc pages without
>> incrementing their refcount, then convert hugetlb cma to use the
>> cma_alloc_frozen_compound() and cma_release_frozen() and remove the
>> unused cma_{alloc,free}_folio(), also move the cma_validate_zones()
>> into mm/internal.h since no outside user.
>>
>> The set_pages_refcounted() is only called to set non-compound pages
>> after above changes, so remove the processing about PageHead.
>>
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>> ---
>>   include/linux/cma.h | 26 ++++++------------------
>>   mm/cma.c            | 48 +++++++++++++++++++++++++--------------------
>>   mm/hugetlb_cma.c    | 24 +++++++++++++----------
>>   mm/internal.h       | 10 +++++-----
>>   4 files changed, 52 insertions(+), 56 deletions(-)
>>

...

>>   static bool __cma_release(struct cma *cma, const struct page *pages,
>> -			  unsigned long count, bool compound)
>> +			  unsigned long count, bool frozen)
>>   {
>>   	unsigned long pfn, end;
>>   	int r;
>> @@ -974,8 +982,8 @@ static bool __cma_release(struct cma *cma, const struct page *pages,
>>   		return false;
>>   	}
>>
>> -	if (compound)
>> -		__free_pages((struct page *)pages, compound_order(pages));
>> +	if (frozen)
>> +		free_contig_frozen_range(pfn, count);
>>   	else
>>   		free_contig_range(pfn, count);
> 
> Can we get rid of free_contig_range() branch by making cma_release() put
> each page’s refcount? Then, __cma_relase() becomes cma_release_frozen()
> and the release pattern matches allocation pattern:
> 1. cma_alloc() calls cma_alloc_frozen() and manipulates page refcount.
> 2. cma_release() manipulates page refcount and calls cma_release_frozen().
> 

Have considered similar things before, but we need manipulates page
refcount only find the correct cma memrange from cma/pages, it seems
that no big improvement, any more comments?

1) for cma_release:
    a. cma find memrange
    b. manipulates page refcount when cmr found
    c. free page and release cma resource
2) for cma_release_frozen
    a. cma find memrange
    b. free page and release cma resource whne cmr found

> The rest of changes looks good to me.

Thanks.
> 
> Best Regards,
> Yan, Zi
>