linux-kernel - Re: [PATCH v9 2/8] mm/huge_memory: add two new (not yet used) functions for folio

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Message-ID: <Z7_-XweaPpfdRz1h@casper.infradead.org>
Date: Thu, 27 Feb 2025 05:55:43 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Zi Yan <ziy@...dia.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Hugh Dickins <hughd@...gle.com>,
	David Hildenbrand <david@...hat.com>,
	Yang Shi <yang@...amperecomputing.com>,
	Miaohe Lin <linmiaohe@...wei.com>,
	Kefeng Wang <wangkefeng.wang@...wei.com>,
	Yu Zhao <yuzhao@...gle.com>, John Hubbard <jhubbard@...dia.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
	Kairui Song <kasong@...cent.com>
Subject: Re: [PATCH v9 2/8] mm/huge_memory: add two new (not yet used)
 functions for folio_split()

On Wed, Feb 26, 2025 at 04:00:25PM -0500, Zi Yan wrote:
> +static int __split_unmapped_folio(struct folio *folio, int new_order,
> +		struct page *split_at, struct page *lock_at,
> +		struct list_head *list, pgoff_t end,
> +		struct xa_state *xas, struct address_space *mapping,
> +		bool uniform_split)
> +{
[...]
> +		/* complete memcg works before add pages to LRU */
> +		split_page_memcg(&folio->page, old_order, split_order);
> +		split_page_owner(&folio->page, old_order, split_order);
> +		pgalloc_tag_split(folio, old_order, split_order);

At least split_page_memcg() needs to become aware of 'uniform_split'.

        if (folio_memcg_kmem(folio))
                obj_cgroup_get_many(__folio_objcg(folio), old_nr / new_nr - 1);

If we're doing uniform_split, that calculation should be
	old_order - new_order - 1