From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 29389CCF9F8 for ; Wed, 12 Nov 2025 11:34:34 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 847948E001A; Wed, 12 Nov 2025 06:34:33 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7F88E8E0003; Wed, 12 Nov 2025 06:34:33 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 70E868E001A; Wed, 12 Nov 2025 06:34:33 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 604748E0003 for ; Wed, 12 Nov 2025 06:34:33 -0500 (EST) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id D4440B98D2 for ; Wed, 12 Nov 2025 11:34:32 +0000 (UTC) X-FDA: 84101747184.16.E865430 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf20.hostedemail.com (Postfix) with ESMTP id 1EF281C0011 for ; Wed, 12 Nov 2025 11:34:30 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="EpsdFkP/"; spf=pass (imf20.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1762947271; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=1WQGRH7KRj0RlgERGH5biPvTuq4UWnPKy8zeURx4as0=; b=onWa0Ql1GXfc7/7JgL2TcIHgXzGHjs9RHnhytSNLJnncVKIQKt7y5BuNmDNRYtmwcceltI 5A2SOJlNmkuAt3v1HnCP3YXvVkakb4/K+nkTpKJRlS3GjzAM0ySW/XdsxUKI8K/1++WqjO NawZ2LyLC6WYr5zciUwvWAoLp5wQJis= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1762947271; a=rsa-sha256; cv=none; b=Tm3FyKtaOvPv3AsNHQ1u943NAD6gFcj3+Nxg6uaAVOkSaan47D5NM2lPNmUBeDKKLWwyGG wNO2AonGG13BJrEIqaA+SMiDCW0uSxkq+M4CMJnE+hyNLTLpygGIAcrrKYIy/5RRMHshDa GoIOTIiwebV2xLi/OuYuwiZS1l68J+Y= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="EpsdFkP/"; spf=pass (imf20.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id D67E341AAF; Wed, 12 Nov 2025 11:34:29 +0000 (UTC) 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 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 X-Stat-Signature: co7iczp6xg8zhh6u84o14u7ikg46nzag X-Rspam-User: X-Rspamd-Queue-Id: 1EF281C0011 X-Rspamd-Server: rspam01 X-HE-Tag: 1762947270-45479 X-HE-Meta: U2FsdGVkX1+jLJ9xdzaYYR3OxtS01lj3/EKoulc5DsTInsoAidnO2XHHweHs07jyMtXJDj8M1FMPgf94g21EVIIqedk7eYjHosGINuDnybvKNzHKzOlDNqsv5oYfP1B4EfMDo+2rklJbvz7lMyxzsOHRR07gvYy8L+bILWkrOfxmLmULvJk25wymD54m38FeEWW19n/Teg3KkYe+h0e7tGEs4VIOxPeYUcjYet4PFPj56fiUe4GTZJDOKQhI0D/aZuKgS0HEJiJGblkKa+CIZS3n5RF6SPcPvodtcH3UCG9FZ5KPAoNvINrd8DYvprIma3c0EOVsk507Cw6bbDCh4ijY6FeCgVJVWBHYfvuOvPbRCtbzKUiuhMpvU2/2iBFhDrMEGwrClNZiD+axBMLj0zoD5wzXStirkuvcLqV6S6diE2xjStvUu3xOaGrhfJcy6i/V6aswfakowHKwebSxwrxzpsozqfZ2HgrjYop0IlhsCsNG6/r/pgu2LmgfdI9gF0JweQBnbTxdSd1YUdqSNzz88CSizV79SSp5XgjiVk0rYuUysYktCpiL1ShK1eLrF8brfrLKSCjrutahheD8vPwokx46J+AJGcKdP3U0dg4MsaRfSWJtK0PigRZ+XyKrFRROMU78spZkjlSI/KqcHd2wh8YqKTc4AkA73bVGX1G3njRDD0rS7Wt8pWie127Rb1cfbQ+IW2u2wI1EJgs9qXGsl6LgT2n9dU2Doek1jPS44n4abbpJ87KQxL9cP1LD/zevMP6DB40nPQT1aBn5hvyOXW4uBZfU8VL/sUQvpZsVMxQ+2fQtPuHMvycdgGwpblRsrYWI2p7awiPdQlugXoziF7qrJhV51uaimPNIErfdcYoHWApH8i5TTs/Ma8j9RBB4scWoccm38+1f20RRU0toq/LKOjCQZtBmKyV6jF36e00YycZbrYs4TEljCqqM78gHKevodeDxh2ASpOx PA2MIF6A 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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