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

[Muchun Song <muchun.song@linux.dev>]

> 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>

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.

> +	if (folio_test_hugetlb(folio) && folio_test_hugetlb_cma(folio))
> +		return true;
> +
> +	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);
> +}
> +
> /*
>  * An array of either pages or folios ("pofs"). Although it may seem tempting to
>  * avoid this complication, by simply interpreting a list of folios as a list of
> -- 
> 2.54.0
>