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 6AA6A2FF658 for ; Wed, 12 Nov 2025 10:00:09 +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=1762941609; cv=none; b=CjfQ6DiVV1e4y47FRzZv49R0fvNwKbW5BLANs2qPeOUbAt77DWOQUciV23QDps+Mr0RTRU+KXA1nbD3l1lbXlKkWMasrBp4sho/sZThO3Ym+L2U6TPlURwh6oQZVx1/m67DSAu8bqeBfla7TuFZ/pxD0eJsvL6GsHI+i9uZ3vkE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762941609; c=relaxed/simple; bh=Hc9SpvODoEKqXyT0Yv/Hs9C9gFsaCYRYLwLn+AbBGok=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cCq+iGYFWtk8CKtvqXW2ETT96wyYuK9SgNincoROryOgLHWuOxMHxb6YjigqA1bSafJQLaHisc0yRIqXKuZX/w/ivfMekBpXvp5/QkiadkcYCWARCmoxGd4z+YHX1wkJkDtp/taKVaNABXgrQq5w2/TJwFlL/GTbtZryYkYhwr4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=akwA/QS5; 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="akwA/QS5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9BB55C4CEF8; Wed, 12 Nov 2025 10:00:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762941608; bh=Hc9SpvODoEKqXyT0Yv/Hs9C9gFsaCYRYLwLn+AbBGok=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=akwA/QS5z6CaUXVEzunr+7pQgnrxiS05TwnBHMPu9G9K7v9c/3R8iUIoq0Fcs1D4g uZyFVcYDoifzu15xZtQHiFBAIMDuqArYYZlBjJXdyvuagQ+WofFYu/yGFfMBt2KwOe G+n6vnPF/RN8DkE0+tTxciwrHE1uEt6TYEil166dlKMJggi3wQvLptrv9X9lU6PxgQ XNAr6Fr9I8+mApELE0Zj+iZ1Qiz442z8ZyH6mke/U0LWo9Hx0HSVCUoO8RPKVSBGnf CUy8XhqDiIhiws23n55El8P4yhgadO8ReX6Eikf6sUhqd0LFCEWkHzOmC++LncJ0+w wQDl9Ia2iQ4lw== Message-ID: <048134fd-6a3d-4a6c-a2eb-9a9911c3b35f@kernel.org> Date: Wed, 12 Nov 2025 11:00:01 +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> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <20251112044634.963360-1-balbirs@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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 ..." > > 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? -- Cheers David