Re: [PATCH v4 2/3] mm: gup: allow long-term pins of CMA-allocated HugeTLB folios

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

On 11/12/26 4:49 PM, David Hildenbrand (Arm) wrote:
> On 11/12/26 07:13, Qi Zheng wrote:
>>
>>
>> On 11/11/26 3:42 PM, Muchun Song 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
>>>
>>> Commit message needs updating to bitmap as well.
>>
>> Will do.
>>
>>>
>>>> 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>
>>>> Reviewed-by: Oscar Salvador <osalvador@suse.de>
>>>> Reviewed-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>
>>>> ---
>>>> 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 b0da9be413098..47d1d96bfc7fd 100644
>>>> --- a/include/linux/mm.h
>>>> +++ b/include/linux/mm.h
>>>> @@ -2954,35 +2954,8 @@ 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)
>>>
>>> I think David prefer to move this function first, then fix it in a separate
>>> patch,
>>> right?
>>
>> Hi David, is this what you mean? If so, I will split it into two patches
>> for the v5.
> 
> Let's try something that is more future-directed: cma should deal with
> cma details. In the future we might implement something reasonable there.

Aha, that does make more sense. Will do.

Thanks,
Qi

> 
> diff --git a/include/linux/cma.h b/include/linux/cma.h
> index 8555d38a97b1a..d829fd0355bae 100644
> --- a/include/linux/cma.h
> +++ b/include/linux/cma.h
> @@ -21,6 +21,9 @@
>   #define CMA_MIN_ALIGNMENT_BYTES (PAGE_SIZE * CMA_MIN_ALIGNMENT_PAGES)
>   
>   struct cma;
> +struct folio;
> +
> +bool cma_folio_is_longterm_pinnable(struct folio *folio);
>   
>   extern unsigned long totalcma_pages;
>   extern phys_addr_t cma_get_base(const struct cma *cma);
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 6af3b7008f1ad..5392e225cab9b 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3,6 +3,7 @@
>   #define _LINUX_MM_H
>   
>   #include <linux/args.h>
> +#include <linux/cma.h>
>   #include <linux/errno.h>
>   #include <linux/mmdebug.h>
>   #include <linux/gfp.h>
> @@ -2975,7 +2976,10 @@ 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 */
> +/*
> + * MIGRATE_CMA and ZONE_MOVABLE folios cannot normally be long-term pinned.
> + * CMA may allow pinning folios explicitly allocated from its areas.
> + */
>   #ifdef CONFIG_MIGRATION
>   static inline bool folio_is_longterm_pinnable(struct folio *folio)
>   {
> @@ -2983,7 +2987,7 @@ static inline bool folio_is_longterm_pinnable(struct folio *folio)
>   	int mt = folio_migratetype(folio);
>   
>   	if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE)
> -		return false;
> +		return cma_folio_is_longterm_pinnable(folio);
>   #endif
>   	/* The zero page can be "pinned" but gets special handling. */
>   	if (is_zero_folio(folio))
> diff --git a/mm/cma.c b/mm/cma.c
> index 9ec1d1fd5dff5..b3bf0014a90f5 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -27,6 +27,7 @@
>   #include <linux/log2.h>
>   #include <linux/cma.h>
>   #include <linux/highmem.h>
> +#include <linux/hugetlb.h>
>   #include <linux/io.h>
>   #include <linux/kmemleak.h>
>   #include <trace/events/cma.h>
> @@ -38,6 +39,16 @@
>   struct cma cma_areas[MAX_CMA_AREAS];
>   unsigned int cma_area_count;
>   
> +bool cma_folio_is_longterm_pinnable(struct folio *folio)
> +{
> +	/*
> +	 * Explicitly allocated CMA folios own their bitmap ranges and can be
> +	 * pinned even in ZONE_MOVABLE, as CMA memory cannot be offlined.
> +	 * For now, only HugeTLB tracks these allocations with a folio flag.
> +	 */
> +	return folio_test_hugetlb(folio) && folio_test_hugetlb_cma(folio);
> +}
> +
>   phys_addr_t cma_get_base(const struct cma *cma)
>   {
>   	WARN_ON_ONCE(cma->nranges != 1);