Re: [PATCH v1] mm/huge_memory: rename __split_unmapped_folio to __split_frozen_folio

[Zi Yan <ziy@nvidia.com>]

On 19 Nov 2025, at 0:46, Jiaqi Yan wrote:

> The correct prerequisite for this split utility isn't really about
> if the folio is unmapped; it is more about after unmapped, folio's
> refcount is zero and has also been frozen. So rename it to
> __split_frozen_folio.
>
> Add a warning in case the folio has non-zero refcount.
>
> No new function is added.
>
> Tested by running split_huge_page_test: testcases all pass and no
> warning is shown in dmesg.

Thank you for doing this.

>
> Suggested-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
> ---
>  mm/huge_memory.c | 20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 2f2a521e5d683..5b9c3725e9265 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3390,7 +3390,7 @@ static void __split_folio_to_order(struct folio *folio, int old_order,
>  }
>
>  /*
> - * It splits an unmapped @folio to lower order smaller folios in two ways.
> + * It splits an frozen @folio to lower order smaller folios in two ways.

s/an/a

>   * @folio: the to-be-split folio
>   * @new_order: the smallest order of the after split folios (since buddy
>   *             allocator like split generates folios with orders from @folio's
> @@ -3428,9 +3428,9 @@ static void __split_folio_to_order(struct folio *folio, int old_order,
>   * For !uniform_split, when -ENOMEM is returned, the original folio might be
>   * split. The caller needs to check the input folio.
>   */
> -static int __split_unmapped_folio(struct folio *folio, int new_order,
> -		struct page *split_at, struct xa_state *xas,
> -		struct address_space *mapping, bool uniform_split)
> +static int __split_frozen_folio(struct folio *folio, int new_order,
> +				struct page *split_at, struct xa_state *xas,
> +				struct address_space *mapping, bool uniform_split)

Hmm, bool uniform_split is changed to enum split_type split_type recently.
Can you rebase your patch on top of mm-new branch at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/?

>  {
>  	int order = folio_order(folio);
>  	int start_order = uniform_split ? new_order : order - 1;
> @@ -3439,6 +3439,8 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
>  	int split_order;
>  	int ret = 0;
>
> +	VM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio) != 0, folio);
> +
>  	if (folio_test_anon(folio))
>  		mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);
>
> @@ -3583,9 +3585,9 @@ bool uniform_split_supported(struct folio *folio, unsigned int new_order,
>   * @list: after-split folios will be put on it if non NULL
>   * @uniform_split: perform uniform split or not (non-uniform split)
>   *
> - * It calls __split_unmapped_folio() to perform uniform and non-uniform split.
> + * It calls __split_frozen_folio() to perform uniform and non-uniform split.
>   * It is in charge of checking whether the split is supported or not and
> - * preparing @folio for __split_unmapped_folio().
> + * preparing @folio for __split_frozen_folio().
>   *
>   * After splitting, the after-split folio containing @lock_at remains locked
>   * and others are unlocked:

This part is also changed on mm-new branch.

> @@ -3698,7 +3700,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
>  		i_mmap_lock_read(mapping);
>
>  		/*
> -		 *__split_unmapped_folio() may need to trim off pages beyond
> +		 *__split_frozen_folio() may need to trim off pages beyond
>  		 * EOF: but on 32-bit, i_size_read() takes an irq-unsafe
>  		 * seqlock, which cannot be nested inside the page tree lock.
>  		 * So note end now: i_size itself may be changed at any moment,
> @@ -3788,8 +3790,8 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
>  		/* lock lru list/PageCompound, ref frozen by page_ref_freeze */
>  		lruvec = folio_lruvec_lock(folio);
>
> -		ret = __split_unmapped_folio(folio, new_order, split_at, &xas,
> -					     mapping, uniform_split);
> +		ret = __split_frozen_folio(folio, new_order, split_at, &xas,
> +					   mapping, uniform_split);
>
>  		/*
>  		 * Unfreeze after-split folios and put them back to the right
> -- 
> 2.52.0.rc1.455.g30608eb744-goog

Thanks.

Best Regards,
Yan, Zi