linux-kernel - Re: [PATCH v2 2/3] mm/huge_memory: allow split shmem large folio to any lower order

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Message-ID: <c50051c1-76c4-4db4-bfee-c0e52389a824@os.amperecomputing.com>
Date: Wed, 22 Jan 2025 09:58:11 -0800
From: Yang Shi <yang@...amperecomputing.com>
To: Zi Yan <ziy@...dia.com>, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 David Hildenbrand <david@...hat.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 Ryan Roberts <ryan.roberts@....com>, Hugh Dickins <hughd@...gle.com>,
 Miaohe Lin <linmiaohe@...wei.com>, Kefeng Wang <wangkefeng.wang@...wei.com>,
 Yu Zhao <yuzhao@...gle.com>, John Hubbard <jhubbard@...dia.com>,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] mm/huge_memory: allow split shmem large folio to
 any lower order

On 1/22/25 8:19 AM, Zi Yan wrote:
> Commit 4d684b5f92ba ("mm: shmem: add large folio support for tmpfs") has
> added large folio support to shmem. Remove the restriction in
> split_huge_page*().

Reviewed-by: Yang Shi <yang@...amperecomputing.com>

>
> Signed-off-by: Zi Yan <ziy@...dia.com>
> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
>   mm/huge_memory.c | 8 +-------
>   1 file changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 3d3ebdc002d5..deb4e72daeb9 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3299,7 +3299,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
>   		/* Some pages can be beyond EOF: drop them from page cache */
>   		if (tail->index >= end) {
>   			if (shmem_mapping(folio->mapping))
> -				nr_dropped++;
> +				nr_dropped += new_nr;
>   			else if (folio_test_clear_dirty(tail))
>   				folio_account_cleaned(tail,
>   					inode_to_wb(folio->mapping->host));
> @@ -3465,12 +3465,6 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
>   			return -EINVAL;
>   		}
>   	} else if (new_order) {
> -		/* Split shmem folio to non-zero order not supported */
> -		if (shmem_mapping(folio->mapping)) {
> -			VM_WARN_ONCE(1,
> -				"Cannot split shmem folio to non-0 order");
> -			return -EINVAL;
> -		}
>   		/*
>   		 * No split if the file system does not support large folio.
>   		 * Note that we might still have THPs in such mappings due to