From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-172.mta1.migadu.com (out-172.mta1.migadu.com [95.215.58.172]) (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 B41181A6822 for ; Sun, 5 Apr 2026 14:09:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775398146; cv=none; b=SH/nHrjtiHObkIX8fksiaq7pndpMkgmymMI3wv+ZSH2Naq/bfwdVMIFFlvuEDg53UAfW3dp1IQVtyQl7uV7AzBJy46jGlwf9sjT5AAj+6Yj3A/HMnm+Wdbe93treKMY7SVW3X+ZcQwf/7hBhY1VjNRV4hWL+9cNIxI4Rb0MCTls= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775398146; c=relaxed/simple; bh=caRwbmMHIZG0HHX2mkDUXoi/VJXx7kdiKPUXFZQNJ6w=; h=Content-Type:Mime-Version:Subject:From:In-Reply-To:Date:Cc: Message-Id:References:To; b=EkVdbnl4W0O1MNq081qT/kGT58IUlxudpsWXNrcnrVUsHOy0V1OtLKtrlfXFfrNvPob0uxgsNEPt77uSoCfvXz/DktSF/THNwCcvAvD2bSa8Sixd4RP/iyKAztEWSpZiWbnFjkmb9DqdigsywxJPeTXR2nqj5v2W54IHyllTKxE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=ti/UUdIM; arc=none smtp.client-ip=95.215.58.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="ti/UUdIM" Content-Type: text/plain; charset=us-ascii DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1775398141; h=from:from: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; bh=ru/lOWBi/C2PKEU6XsdVIKohFqyMme0d0YkWPc7ryWU=; b=ti/UUdIMVJ/L77ns1IFATic5sd67VGirPPwFVeh2ChB1vvU6+0LX549PWQjIUa0s5MSvUX 4wfN/TOFjh7RnYlMHjYQtScz6lPIMXl5Jk+JzO/cVnEonVr2zW2A/EncPAYvx9shQCKk/E oZ9v3G4ckYdg0ZOQgCmk1b3ivUj+Q8Y= Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3864.500.181\)) Subject: Re: [PATCH v2 1/5] mm/sparse-vmemmap: provide generic vmemmap_set_pmd() and vmemmap_check_pmd() X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Muchun Song In-Reply-To: Date: Sun, 5 Apr 2026 22:07:36 +0800 Cc: Muchun Song , Andrew Morton , David Hildenbrand , linux-mm@kvack.org, Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: References: <20260404122105.3989557-1-songmuchun@bytedance.com> <20260404122105.3989557-2-songmuchun@bytedance.com> To: Mike Rapoport X-Migadu-Flow: FLOW_OUT > On Apr 5, 2026, at 15:07, Mike Rapoport wrote: >=20 > Hi, >=20 > On Sat, Apr 04, 2026 at 08:20:54PM +0800, Muchun Song wrote: >> The two weak functions are currently no-ops on every architecture, >> forcing each platform that needs them to duplicate the same handful >> of lines. Provide a generic implementation: >>=20 >> - vmemmap_set_pmd() simply sets a huge PMD with PAGE_KERNEL = protection. >>=20 >> - vmemmap_check_pmd() verifies that the PMD is present and leaf, >> then calls the existing vmemmap_verify() helper. >>=20 >> Architectures that need special handling can continue to override the >> weak symbols; everyone else gets the standard version for free. >>=20 >> Signed-off-by: Muchun Song >> --- >> mm/sparse-vmemmap.c | 7 ++++++- >> 1 file changed, 6 insertions(+), 1 deletion(-) >>=20 >> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c >> index 6eadb9d116e4..1eb990610d50 100644 >> --- a/mm/sparse-vmemmap.c >> +++ b/mm/sparse-vmemmap.c >> @@ -391,12 +391,17 @@ int __meminit vmemmap_populate_hvo(unsigned = long addr, unsigned long end, >> void __weak __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node, >> unsigned long addr, unsigned long next) >> { >> + BUG_ON(!pmd_set_huge(pmd, virt_to_phys(p), PAGE_KERNEL)); >=20 > Do we have to crash the kernel here? > Wouldn't be better to make vmemmap_set_pmd() return error and make > vmemmap_populate_hugepages() fall back to base pages in case > vmemmap_set_pmd() errored? Hi Mike, Thanks for the review. Let me explain my original thought process here. My assumption was that pmd_set_huge() for the kernel virtual address = space should rarely, if ever, fail in this context. Furthermore, if we look at = the architectures this patch replaces (e.g., arm64 and riscv), they are = either ignoring the return value of pmd_set_huge() entirely or lacking any = graceful fallback mechanism anyway. So, to keep the initial generic implementation as simple as possible, I = used BUG_ON() as a strict assertion. Do you think we really need to introduce a more flexible, = fallback-capable solution at this stage? Based on the current architecture = implementations, it might not be strictly necessary right now. We could keep it simple and = add the error handling/fallback logic in the future if more architectures start = using this generic code and actually require error handling. However, I am completely open to your suggestion. If you feel it's = better to be proactive and make the generic vmemmap_set_pmd() return an error code, = allowing vmemmap_populate_hugepages() to gracefully fall back to base pages right = from the start, I totally agree and will be happy to update it in v3. Please let me know your thoughts. Thanks, Muchun >=20 >> } >>=20 >> int __weak __meminit vmemmap_check_pmd(pmd_t *pmd, int node, >> unsigned long addr, unsigned long next) >> { >> - return 0; >> + if (!pmd_leaf(pmdp_get(pmd))) >> + return 0; >> + vmemmap_verify((pte_t *)pmd, node, addr, next); >> + >> + return 1; >> } >>=20 >> int __meminit vmemmap_populate_hugepages(unsigned long start, = unsigned long end, >> --=20 >> 2.20.1 >>=20 >=20 > --=20 > Sincerely yours, > Mike.