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

[Qi Zheng]

On 11/5/26 1:13 PM, Muchun Song wrote:
> > On Nov 5, 2026, at 12:07, Qi Zheng <qi.zheng@xxxxxxxxx> wrote:
> >
> > From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxxxx
> > Suggested-by: Muchun Song <muchun.song@xxxxxxxxx>
> > Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
>
> Acked-by: Muchun Song <muchun.song@xxxxxxxxx>

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