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

Wei Yang
2025-11-01T00:08:50Z

On Fri, Oct 31, 2025 at 07:52:28PM -0400, Zi Yan wrote:
>On 31 Oct 2025, at 19:36, Wei Yang wrote:
>
>> 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).
>
>Hi Andrew,
>
>Do you mind applying this fixup to address Wei's concerns?
>
>Thanks.
>
>From e1894a4e7ac95bdfe333cf5bee567f0ff90ddf5d Mon Sep 17 00:00:00 2001
>From: Zi Yan <ziy@nvidia.com>
>Date: Fri, 31 Oct 2025 19:50:55 -0400
>Subject: [PATCH] mm/huge_memory: kernel-doc fixup
>
>Signed-off-by: Zi Yan <ziy@nvidia.com>
>---
> mm/huge_memory.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
>diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>index ad2fc52651a6..a30fee2001b5 100644
>--- a/mm/huge_memory.c
>+++ b/mm/huge_memory.c
>@@ -3586,7 +3586,7 @@ static void __split_folio_to_order(struct folio *folio, int old_order,
> * uniform_split is true.
> * 2. buddy allocator like (non-uniform) split: the given @folio is split into
> * half and one of the half (containing the given page) is split into half
>- * until the given @page's order becomes @new_order. This is done when
>+ * until the given @folio's order becomes @new_order. This is done when
> * uniform_split is false.
> *
> * The high level flow for these two methods are:
>@@ -3595,14 +3595,14 @@ static void __split_folio_to_order(struct folio *folio, int old_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
>- * split in each iteration. @xas is split into half in each iteration and
>+ * the @folio to one lower order at a time. The folio containing @split_at
>+ * is 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
>- * folios if necessary.
>+ * folio containing @split_at. The caller needs to unlock and/or free
>+ * after-split folios if necessary.
> *
> * Return: 0 - successful, <0 - failed (if -ENOMEM is returned, @folio might be
> * split but not to @new_order, the caller needs to check)
>--
>2.51.0
>
>

Thanks.

Reviewed-by: Wei Yang <richard.weiyang@gmail.com>

>
>
>--
>Best Regards,
>Yan, Zi

--
Wei Yang
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