Re: [PATCH v5 3/3] mm/huge_memory: fix kernel-doc comments for folio_split() and related.

Wei Yang
2025-10-31T23:36:13Z

On Fri, Oct 31, 2025 at 12:20:01PM -0400, Zi Yan wrote:
[...]
>diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>index 0e24bb7e90d0..ad2fc52651a6 100644
>--- a/mm/huge_memory.c
>+++ b/mm/huge_memory.c
>@@ -3567,8 +3567,9 @@ static void __split_folio_to_order(struct folio *folio, int old_order,
> ClearPageCompound(&folio->page);
> }
>
>-/*
>- * It splits an unmapped @folio to lower order smaller folios in two ways.
>+/**
>+ * __split_unmapped_folio() - splits an unmapped @folio to lower order folios in
>+ * two ways: uniform split or non-uniform split.
> * @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
>@@ -3589,22 +3590,22 @@ static void __split_folio_to_order(struct folio *folio, int old_order,
> * uniform_split is false.
> *
> * The high level flow for these two methods are:
>- * 1. uniform split: a single __split_folio_to_order() is called to split the
>- * @folio into @new_order, then we traverse all the resulting folios one by
>- * one in PFN ascending order and perform stats, unfreeze, adding to list,
>- * and file mapping index operations.
>- * 2. non-uniform split: in general, folio_order - @new_order calls to
>- * __split_folio_to_order() are made in a for loop to split the @folio
>- * to one lower order at a time. The resulting small folios are processed
>- * like what is done during the traversal in 1, except the one containing
>- * @page, which is split in next for loop.
>+ * 1. uniform split: @xas is split with no expectation of failure and a single
>+ * __split_folio_to_order() is called to split the @folio into @new_order
>+ * along with stats update.
>+ * 2. non-uniform split: folio_order - @new_order calls to
>+ * __split_folio_to_order() are expected to be made in a for loop to split
>+ * the @folio to one lower order at a time. The folio containing @page is

Hope it is not annoying.

The parameter's name is @split_at, maybe we misuse it?

s/containing @page/containing @split_at/

>+ * split in each iteration. @xas is split into half in each iteration and
>+ * can fail. A failed @xas split leaves split folios as is without merging
>+ * them back.
> *
> * After splitting, the caller's folio reference will be transferred to the
> * folio containing @page. The caller needs to unlock and/or free after-split

The same above.

And probably there is another one in above this comment(not shown here).

> * folios if necessary.
> *
>- * For !uniform_split, when -ENOMEM is returned, the original folio might be
>- * split. The caller needs to check the input folio.
>+ * Return: 0 - successful, <0 - failed (if -ENOMEM is returned, @folio might be
>+ * split but not to @new_order, the caller needs to check)
> */
> static int __split_unmapped_folio(struct folio *folio, int new_order,
> struct page *split_at, struct xa_state *xas,

--
Wei Yang
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