linux-kernel - Re: [PATCH v3 1/4] mm/huge_memory: change folio_split_supported() to folio_check

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Message-ID: <CAGsJ_4xyFnFefTS6QAC3YnUdm56_HJvxzrTD=bWP5LZqHk0SEg@mail.gmail.com>
Date: Thu, 27 Nov 2025 13:23:00 +0800
From: Barry Song <21cnbao@...il.com>
To: Zi Yan <ziy@...dia.com>
Cc: David Hildenbrand <david@...nel.org>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, 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>, 
	Lance Yang <lance.yang@...ux.dev>, Miaohe Lin <linmiaohe@...wei.com>, 
	Naoya Horiguchi <nao.horiguchi@...il.com>, Wei Yang <richard.weiyang@...il.com>, 
	Balbir Singh <balbirs@...dia.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/4] mm/huge_memory: change folio_split_supported() to folio_check_splittable()

On Wed, Nov 26, 2025 at 11:50 AM Zi Yan <ziy@...dia.com> wrote:
>
> folio_split_supported() used in try_folio_split_to_order() requires
> folio->mapping to be non NULL, but current try_folio_split_to_order() does
> not check it. There is no issue in the current code, since
> try_folio_split_to_order() is only used in truncate_inode_partial_folio(),
> where folio->mapping is not NULL.
>
> To prevent future misuse, move folio->mapping NULL check (i.e., folio is
> truncated) into folio_split_supported(). Since folio->mapping NULL check
> returns -EBUSY and folio_split_supported() == false means -EINVAL, change
> folio_split_supported() return type from bool to int and return error
> numbers accordingly. Rename folio_split_supported() to
> folio_check_splittable() to match the return type change.
>
> While at it, move is_huge_zero_folio() check and folio_test_writeback()
> check into folio_check_splittable() and add kernel-doc.
>
> Remove all warnings inside folio_check_splittable() and give warnings
> in __folio_split() instead, so that bool warns parameter can be removed.
>
> Signed-off-by: Zi Yan <ziy@...dia.com>
> Reviewed-by: Wei Yang <richard.weiyang@...il.com>

Much cleaner than having a "warns" argument before.

Reviewed-by: Barry Song <baohua@...nel.org>

Thanks
Barry