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

[Zi Yan <ziy@nvidia.com>]

On 18 Dec 2025, at 7:54, Kefeng Wang wrote:

> On 2025/12/18 3:38, Zi Yan wrote:
>> On 17 Dec 2025, at 3:02, Kefeng Wang wrote:
>>
>>> 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
>>
>> Right, I think it makes code simpler.
>>
>> Basically add a helper function:
>> struct cma_memrange* find_cma_memrange(struct cma *cma,
>> 		const struct page *pages, unsigned long count);
>>
>> Then
>>
>> __cma_release_frozen()
>> {
>> 	free_contig_frozen_range(pfn, count);
>> 	cma_clear_bitmap(cma, cmr, pfn, count);
>> 	cma_sysfs_account_release_pages(cma, count);
>> 	trace_cma_release(cma->name, pfn, pages, count);
>> }
>>
>>
>> cma_release()
>> {
>> 	cmr = find_cma_memrange();
>>
>> 	if (!cmr)
>> 		return false;
>> 	
>> 	for (; count--; pages++)
>> 		VM_WARN_ON(!put_page_testzero(pages);
>>
>> 	__cma_release_frozen();
>> }
>>
>> cma_release_frozen()
>> {
>> 	cmr = find_cma_memrange();
>>
>> 	if (!cmr)
>> 		return false;
>>
>> 	__cma_release_frozen();
>>
>> }
>>
>> Let me know your thoughts.
>
> Yes, this is exactly what I described above that needs to be done, but I
> think it will add more codes :)
>
> Our goal is that convert all cma_{alloc,release} caller to
> cma_frozen_{alloc,release}, and complete remove free_contig_range in cma, Maybe no changes? But if you prefer above way, I can also update
> it.

If the goal is to replace all cma_{alloc,release}() calls with the frozen version,
there is no need to make the change as I suggested. Are you planning to send
another patchset to do the replacement after this one?

Best Regards,
Yan, Zi