Re: [PATCH v2 2/4] mm: gup: allow long-term pins of CMA-allocated HugeTLB folios

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

On 11/5/26 1:13 PM, Muchun Song wrote:
> 
> 
>> On Nov 5, 2026, at 12:07, Qi Zheng <qi.zheng@linux.dev> wrote:
>>
>> From: Qi Zheng <zhengqi.arch@bytedance.com>
>>
>> Long-term pinning treats explicitly CMA-allocated HugeTLB folios as
>> unpinnable, causing unnecessary migration or pinning failures.
>>
>> These folios already own their CMA bitmap ranges, and memory blocks
>> overlapping CMA areas cannot be offlined. Allow HugeTLB folios with
>> HPG_cma to be pinned directly, including in ZONE_MOVABLE.
>>
>> Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma")
>> Cc: stable@vger.kernel.org
>> Suggested-by: Muchun Song <muchun.song@linux.dev>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> Acked-by: Muchun Song <muchun.song@linux.dev>

Thanks.

> 
> But a nit bellow.
> 
>> ---
>> include/linux/mm.h | 29 +----------------------------
>> mm/gup.c           | 31 +++++++++++++++++++++++++++++++
>> 2 files changed, 32 insertions(+), 28 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 2d0b8a4c9974f..75dd40265d3f4 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2975,35 +2975,8 @@ static inline bool is_zero_folio(const struct folio *folio)
>> 	return is_zero_page(&folio->page);
>> }
>>
>> -/* MIGRATE_CMA and ZONE_MOVABLE do not allow pin folios */
>> #ifdef CONFIG_MIGRATION
>> -static inline bool folio_is_longterm_pinnable(struct folio *folio)
>> -{
>> -#ifdef CONFIG_CMA
>> -	int mt = folio_migratetype(folio);
>> -
>> -	if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE)
>> -		return false;
>> -#endif
>> -	/* The zero page can be "pinned" but gets special handling. */
>> -	if (is_zero_folio(folio))
>> -		return true;
>> -
>> -	/* Coherent device memory must always allow eviction. */
>> -	if (folio_is_device_coherent(folio))
>> -		return false;
>> -
>> -	/*
>> -	 * Filesystems can only tolerate transient delays to truncate and
>> -	 * hole-punch operations
>> -	 */
>> -	if (folio_is_fsdax(folio))
>> -		return false;
>> -
>> -	/* Otherwise, non-movable zone folios can be pinned. */
>> -	return !folio_is_zone_movable(folio);
>> -
>> -}
>> +bool folio_is_longterm_pinnable(struct folio *folio);
>> #else
>> static inline bool folio_is_longterm_pinnable(struct folio *folio)
>> {
>> diff --git a/mm/gup.c b/mm/gup.c
>> index 2b405cce2ca5c..e8503141bb275 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -2216,6 +2216,37 @@ struct page *get_dump_page(unsigned long addr, int *locked)
>>
>> #ifdef CONFIG_MIGRATION
>>
>> +bool folio_is_longterm_pinnable(struct folio *folio)
>> +{
>> +#ifdef CONFIG_CMA
>> +	int mt = folio_migratetype(folio);
>> +
>> +	/* Explicit HugeTLB CMA allocations own their bitmap ranges. */
> 
> The description of "bitmap ranges" is weird, making me think what's the meaning of
> bitmap. Please use more generic description here.

How about this:

/* These HugeTLB folios own the CMA memory, so they can be long-term 
pinned. */

Thanks,
Qi