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

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

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.

Thanks