From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 25B9E30EF71 for ; Wed, 12 Nov 2025 11:34:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762947270; cv=none; b=C3WB+nZhJzSx81joF3I2b6YrEm8pxcLyP/mzEL0GpDPbsDfNtOWnRBY9lT6uyBc4Lkf1y8WIdV3FXD+DKclccro56HDCO6ZwDMXuLK+WKB4TSqOvC8wHvaTxXwxGF0DfL3MF/riuPMtr7NJzj2BHiO9vBQktVVd+iqGnSONjAlQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762947270; c=relaxed/simple; bh=rAhECoWyxD/5mXaMjAqq2GVzvYlNQTIj7BGyaTujbEc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IjWLBWG3k6N4ePXDvVrx80r6DEP7YBjoHh5VuZ/IgEgidtU8C+UIRMMiSZyojP4SKkdGQtS9th5TPiKSUZWiBTr/CfuV2gqpdtnNetTS96dirfipT1mE7FIujKPrnooCWogAvsgaNa+pqKJcaSIfvN/YQih61YlEbvXIQPI78EM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EpsdFkP/; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="EpsdFkP/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 96FD7C4CEF5; Wed, 12 Nov 2025 11:34:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762947269; bh=rAhECoWyxD/5mXaMjAqq2GVzvYlNQTIj7BGyaTujbEc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=EpsdFkP/HSPMUyE75qXCFNFWREmp6aDwYXrqWGnHUDTd8l9G57vGIQkZCpqTldbe8 Wq3NemyJQYf3yz3cy+1bZogBnxlVXDFfM5C5TlNoQWh+0eKG2q0xQIRfEZbm+ZfCw+ DEABNOWriB4d4Vns/BFpn0B+73GB2rmEchf5PLehQFa2lW28Tc6EJLtp9KAlTOtIOh 1ME4IZ515mBuKI3BSFGS4sKDmcUSlL7Vt/2Xz5pQn8m5xBcB3leGw4Z1gvLE8o7bfK /KcLe4kCf30H/2kFg4AT08/Mf/BfYQlt0OrtI3HNKxQR2Xfer2TKovKzjJzoQMpEzR /NlGXfYC+LFQQ== Message-ID: <826df5b1-b61d-4794-a96c-dcf9ac19e269@kernel.org> Date: Wed, 12 Nov 2025 12:34:22 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/huge_memory.c: introduce split_unmapped_folio_to_order To: Balbir Singh , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Zi Yan , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Oscar Salvador , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , Ralph Campbell , =?UTF-8?Q?Mika_Penttil=C3=A4?= , Matthew Brost , Francois Dugast References: <20251112044634.963360-1-balbirs@nvidia.com> <048134fd-6a3d-4a6c-a2eb-9a9911c3b35f@kernel.org> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 12.11.25 11:17, Balbir Singh wrote: > On 11/12/25 21:00, David Hildenbrand (Red Hat) wrote: >> On 12.11.25 05:46, Balbir Singh wrote: >>> Unmapped was added as a parameter to __folio_split() and related >>> call sites to support splitting of folios already in the midst >>> of a migration. This special case arose for device private folio >>> migration since during migration there could be a disconnect between >>> source and destination on the folio size. >>> >>> Introduce split_unmapped_folio_to_order() to handle this special case. >>> This in turn removes the special casing introduced by the unmapped >>> parameter in __folio_split(). >> >> As raised recently, I would hope that we can find a way to make all these splitting functions look more similar in the long term, ideally starting with "folio_split" / "folio_try_split". >> >> What about >> >>     folio_split_unmapped() >> >> Do we really have to spell out the "to order" part in the function name? >> >> And if it's more a mostly-internal helper, maybe >> >>     __folio_split_unmapped() >> >> subject: "mm/huge_memory: introduce ..." >> > > I can rename it, but currently it confirms to the split_folio with order in the name > The order is there in the name because in the future with mTHP we will want to > support splitting to various orders. I think we should start naming them more consistently regarding folio_split() immediately and cleanup the other ones later. I don't understand why "_to_order" must be in the name right now. You can add another variant and start using longer names when really required. > > >>> >>> Cc: Andrew Morton >>> Cc: David Hildenbrand >>> Cc: Zi Yan >>> Cc: Joshua Hahn >>> Cc: Rakie Kim >>> Cc: Byungchul Park >>> Cc: Gregory Price >>> Cc: Ying Huang >>> Cc: Alistair Popple >>> Cc: Oscar Salvador >>> Cc: Lorenzo Stoakes >>> Cc: Baolin Wang >>> Cc: "Liam R. Howlett" >>> Cc: Nico Pache >>> Cc: Ryan Roberts >>> Cc: Dev Jain >>> Cc: Barry Song >>> Cc: Lyude Paul >>> Cc: Danilo Krummrich >>> Cc: David Airlie >>> Cc: Simona Vetter >>> Cc: Ralph Campbell >>> Cc: Mika Penttilä >>> Cc: Matthew Brost >>> Cc: Francois Dugast >>> >>> Suggested-by: Zi Yan >>> Signed-off-by: Balbir Singh >>> --- >>>   include/linux/huge_mm.h |   5 +- >>>   mm/huge_memory.c        | 135 ++++++++++++++++++++++++++++++++++------ >>>   mm/migrate_device.c     |   3 +- >>>   3 files changed, 120 insertions(+), 23 deletions(-) >>> >>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >>> index e2e91aa1a042..9155e683c08a 100644 >>> --- a/include/linux/huge_mm.h >>> +++ b/include/linux/huge_mm.h >>> @@ -371,7 +371,8 @@ enum split_type { >>>     bool can_split_folio(struct folio *folio, int caller_pins, int *pextra_pins); >>>   int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list, >>> -        unsigned int new_order, bool unmapped); >>> +        unsigned int new_order); >>> +int split_unmapped_folio_to_order(struct folio *folio, unsigned int new_order); >>>   int min_order_for_split(struct folio *folio); >>>   int split_folio_to_list(struct folio *folio, struct list_head *list); >>>   bool folio_split_supported(struct folio *folio, unsigned int new_order, >>> @@ -382,7 +383,7 @@ int folio_split(struct folio *folio, unsigned int new_order, struct page *page, >>>   static inline int split_huge_page_to_list_to_order(struct page *page, struct list_head *list, >>>           unsigned int new_order) >>>   { >>> -    return __split_huge_page_to_list_to_order(page, list, new_order, false); >>> +    return __split_huge_page_to_list_to_order(page, list, new_order); >>>   } >>>   static inline int split_huge_page_to_order(struct page *page, unsigned int new_order) >>>   { >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index 0184cd915f44..942bd8410c54 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -3747,7 +3747,6 @@ bool folio_split_supported(struct folio *folio, unsigned int new_order, >>>    * @lock_at: a page within @folio to be left locked to caller >>>    * @list: after-split folios will be put on it if non NULL >>>    * @split_type: perform uniform split or not (non-uniform split) >>> - * @unmapped: The pages are already unmapped, they are migration entries. >>>    * >>>    * It calls __split_unmapped_folio() to perform uniform and non-uniform split. >>>    * It is in charge of checking whether the split is supported or not and >>> @@ -3763,7 +3762,7 @@ bool folio_split_supported(struct folio *folio, unsigned int new_order, >>>    */ >>>   static int __folio_split(struct folio *folio, unsigned int new_order, >>>           struct page *split_at, struct page *lock_at, >>> -        struct list_head *list, enum split_type split_type, bool unmapped) >>> +        struct list_head *list, enum split_type split_type) >> >> Yeah, nice to see that go. >> >>>   { >>>       struct deferred_split *ds_queue; >>>       XA_STATE(xas, &folio->mapping->i_pages, folio->index); >>> @@ -3809,14 +3808,12 @@ static int __folio_split(struct folio *folio, unsigned int new_order, >>>            * is taken to serialise against parallel split or collapse >>>            * operations. >>>            */ >>> -        if (!unmapped) { >>> -            anon_vma = folio_get_anon_vma(folio); >>> -            if (!anon_vma) { >>> -                ret = -EBUSY; >>> -                goto out; >>> -            } >>> -            anon_vma_lock_write(anon_vma); >>> +        anon_vma = folio_get_anon_vma(folio); >>> +        if (!anon_vma) { >>> +            ret = -EBUSY; >>> +            goto out; >>>           } >>> +        anon_vma_lock_write(anon_vma); >>>           mapping = NULL; >>>       } else { >>>           unsigned int min_order; >>> @@ -3882,8 +3879,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order, >>>           goto out_unlock; >>>       } >>>   -    if (!unmapped) >>> -        unmap_folio(folio); >>> +    unmap_folio(folio); >>> >> >> Hm, I would have hoped that we could factor out the core logic and reuse it for the new helper, instead of duplicating code. >> >> Did you look into that? >> >> > > I did, I ended up with larger spaghetti, I was hoping to look it as a follow up > after the series with the mTHP changes and support (that is to be designed and > prototyped). Looking at it in more detail, the code duplication is not desired. We have to find a way to factor the existing code out and reuse it from any new function. -- Cheers David