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 26BBE1D555 for ; Mon, 24 Nov 2025 10:33:55 +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=1763980435; cv=none; b=ojP3+lyUBsiedx42uK330DqjznX5+ERAxBtFcyCbp/5viRWpCqOOXCBFu0/8pdRfexq7LvN5f+aCK9RFZyk8XrDlbGnoy1BDaeevPXkCohWBi4U5SfbybAIGVxxYjL7TTPB0IULl4XjDANZTkhPDlQd2E9zZ9YrDKfRHg78m2Qo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763980435; c=relaxed/simple; bh=9yc7x0NqELzfUZMjCX5AI1V6GWkCqxsRDtJfN0ylbjU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qvByFsptTCHztE6hvybtBYTljmTyQNEBz2ugAvZ2as5Beq0y5QLIbo7svxLjxjDiVih58dtNSL/Yjf+F/9h6ppiKjuzXJPmkZqge4f6AME05nh9qeYMG7jU82WJL9eM7RM781n8pYTtQnm3DJvfSUfL7l2MimhLIrW896zPFYww= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FGYHbnAn; 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="FGYHbnAn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C8F53C4CEF1; Mon, 24 Nov 2025 10:33:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763980435; bh=9yc7x0NqELzfUZMjCX5AI1V6GWkCqxsRDtJfN0ylbjU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=FGYHbnAntD/Scnr8pk77Bv9rQzRW5wcuSrEuoXLix2iy51nsKDW1u0vePbaqTB7qa JI8G8qvKqDrj9UfD9hRUXFJUngeyXztymXaXmUfYNrqVZEpSsA2DZgL7S4ELTD2YIB Dug8PyMOHOzmsBPbrXcvwda9TgheSHHHnjStW3ZO9Aicky/58YLWi+MiNKegvfa+Va UDKBE999phJttg/sqB8Ug+G6zDIEThIGes4vxcZoGvxMfMobpDCViJuGuQr58LJwc8 uyzytistiLPgb2kMWVW/Fq7q6zzyCNbywj4ZBZlHHGjlLrg3UelGyed9Upyp4AGKgv gG7BHcYrl3EAg== Message-ID: <60d27f00-20ca-4a58-9d32-ffbe55f69a1d@kernel.org> Date: Mon, 24 Nov 2025 11:33:47 +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 v2 1/4] mm/huge_memory: change folio_split_supported() to folio_check_splittable() To: Barry Song <21cnbao@gmail.com>, Zi Yan Cc: Lorenzo Stoakes , Andrew Morton , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Lance Yang , Miaohe Lin , Naoya Horiguchi , Wei Yang , Balbir Singh , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20251122025529.1562592-1-ziy@nvidia.com> <20251122025529.1562592-2-ziy@nvidia.com> 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 11/23/25 19:38, Barry Song wrote: > Hi Zi Yan, > > Thanks for the nice cleanup. > > On Sat, Nov 22, 2025 at 10:55 AM Zi Yan wrote: >> >> folio_split_supported() used in try_folio_split_to_order() requires >> folio->mapping to be non NULL, but current try_folio_split_to_order() does >> not check it. There is no issue in the current code, since >> try_folio_split_to_order() is only used in truncate_inode_partial_folio(), >> where folio->mapping is not NULL. >> >> To prevent future misuse, move folio->mapping NULL check (i.e., folio is >> truncated) into folio_split_supported(). Since folio->mapping NULL check >> returns -EBUSY and folio_split_supported() == false means -EINVAL, change >> folio_split_supported() return type from bool to int and return error >> numbers accordingly. Rename folio_split_supported() to >> folio_check_splittable() to match the return type change. >> >> While at it, move is_huge_zero_folio() check and folio_test_writeback() >> check into folio_check_splittable() and add kernel-doc. >> >> Signed-off-by: Zi Yan >> --- >> include/linux/huge_mm.h | 10 ++++-- >> mm/huge_memory.c | 74 +++++++++++++++++++++++++---------------- >> 2 files changed, 53 insertions(+), 31 deletions(-) >> >> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >> index 1d439de1ca2c..97686fb46e30 100644 >> --- a/include/linux/huge_mm.h >> +++ b/include/linux/huge_mm.h >> @@ -375,8 +375,8 @@ int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list >> int folio_split_unmapped(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, >> - enum split_type split_type, bool warns); >> +int folio_check_splittable(struct folio *folio, unsigned int new_order, >> + enum split_type split_type, bool warns); > > > It feels a bit odd to have a warns parameter here, especially given that it's > a bool. I understand that in one case we're only checking whether a split is > possible, without actually performing it. In the other case, we are performing > the split, so we must confirm it's valid — otherwise it's a bug. > > Could we rename split_type to something more like gfp_flags, where we have > variants such as __GFP_NOWARN or something similar? That would make the code > much more readable. Could we get rid of the "warns" parameter and simply always do a pr_warn_once()? As an alternative, simply move the warning to the single caller VM_WARN_ONCE(ret == -EINVAL, "Tried to split an unsplittable folio"); -- Cheers David