Message-ID: <20251101000847.3ht26lmiug6aznsh@master>
Date: Sat, 1 Nov 2025 00:08:47 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Zi Yan <ziy@...dia.com>
Cc: akpm@...ux-foundation.org, Wei Yang <richard.weiyang@...il.com>,
	linmiaohe@...wei.com, david@...hat.com, jane.chu@...cle.com,
	kernel@...kajraghav.com, mcgrof@...nel.org, nao.horiguchi@...il.com,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
	Lance Yang <lance.yang@...ux.dev>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Yang Shi <shy828301@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v5 3/3] mm/huge_memory: fix kernel-doc comments for
 folio_split() and related.

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@...dia.com>
>Date: Fri, 31 Oct 2025 19:50:55 -0400
>Subject: [PATCH] mm/huge_memory: kernel-doc fixup
>
>Signed-off-by: Zi Yan <ziy@...dia.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@...il.com>

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

-- 
Wei Yang
Help you, Help me

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