From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-100.mta1.migadu.com [95.215.58.100]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 44879468C26 for ; Thu, 8 Oct 2026 08:16:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.100 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791447425; cv=none; b=UGy5sr1UeOX5Bq9OIxkrH3a0NGIMwH6Oe6E2MGG9zCAJXniNm7qZ0MHpNSe53xD6TlBl3orwK0bNm4S3qRFeJMGu8T2WSMf6X+mRqfjAgU6kMCxs09Ulp/bj3TaGPBoSt3gpO1fJ1P0rFjW7TjUFpx+fGZ7YSKxpguv8UWOK8sM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791447425; c=relaxed/simple; bh=MHAPwba2bGTS8af5kSWYut1fycRyI5aoznVbcbDNoEY=; h=Content-Type:Mime-Version:Subject:From:In-Reply-To:Date:Cc: Message-Id:References:To; b=fN/tz6HEIb3bFeFJSWWz2gsrdlJDjKnEEWs1M9fBgh7eyuBFeaoSYaQ1q1O1f+SKJYbJ9dVpr1aYaG4nuPFAAJC9Evw52hFr5kvz9xYb/FdavbkI9dg9w3VEXy/PIKUjeaduQum2ZYYF+HTNUjl+dNY/X52te6sQYH90KiTUCmc= 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=BkJY+0QS; arc=none smtp.client-ip=95.215.58.100 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="BkJY+0QS" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=MHAPwba2bGTS8af5kSWYut1fycRyI5aoznVbcbDNoEY=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1791447411; v=1; x=1792052211; b=BkJY+0QSb2PH8p++GP4mjbq/HTFXm3+f5i36xosvBRk3rKj/t6A+Zf9vTPO0ab3uN82FxXOs 4FLjSIpaL/NTT7gDSHZCCHiXwebn3WT+VNicvpy/TSH/XW+Ggg3P7v01nSZjBj+rcvWnub7bOId bpVdqVmv+ZmiprT5PjTWaEaQ= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 5d61374c685aff04; Thu, 08 Oct 2026 08:16:50 +0000 X-Mizu-Trace-ID: 5d61374c685aff04 X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset=utf-8 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 \(3901.100.1.1.12\)) Subject: Re: [PATCH v3 6/6] mm/mm_init: add zone mismatch warning during page init From: Muchun Song In-Reply-To: Date: Thu, 8 Oct 2026 10:16:36 +0200 Cc: Muchun Song , Madhavan Srinivasan , Andrew Morton , David Hildenbrand , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Ritesh Harjani , Shrikanth Hegde , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Qi Zheng , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Transfer-Encoding: quoted-printable Message-Id: <3466BD00-1B0E-4F15-B104-88A22807ECD2@linux.dev> References: <20260929053231.66085-1-songmuchun@bytedance.com> <20260929053231.66085-7-songmuchun@bytedance.com> <78D5D6AA-BE36-432C-B0F7-453F93DF18C0@linux.dev> <85941AA4-7E50-4AAE-BC05-0F443B21BE8B@linux.dev> To: Mike Rapoport X-Mailer: Apple Mail (2.3901.100.1.1.12) > On Oct 8, 2026, at 09:45, Mike Rapoport wrote: >=20 > On Tue, Oct 06, 2026 at 03:32:43PM +0200, Muchun Song wrote: >>> On Oct 6, 2026, at 12:52, Mike Rapoport wrote: >>>=20 >>> On Mon, Oct 05, 2026 at 06:27:52PM +0200, Muchun Song wrote: >>>>> On Oct 2, 2026, at 20:12, Mike Rapoport wrote: >>>>>=20 >>>>> On Fri, Oct 02, 2026 at 05:56:40PM +0800, Muchun Song wrote: >>>>>>> On Oct 2, 2026, at 16:22, Mike Rapoport wrote: >>>>>>=20 >>>>>>>>>> diff --git a/mm/mm_init.c b/mm/mm_init.c >>>>>>>>>> index 1650d6bc1211..bd02e8d06965 100644 >>>>>>>>>> --- a/mm/mm_init.c >>>>>>>>>> +++ b/mm/mm_init.c >>>>>>>>>> @@ -609,6 +609,9 @@ void __meminit __init_single_page(struct = page *page, unsigned long pfn, >>>>>>>>>> if (!is_highmem_idx(zone)) >>>>>>>>>> set_page_address(page, __va(pfn << PAGE_SHIFT)); >>>>>>>>>> #endif >>>>>>>>>> + = VM_WARN_ON_ONCE(vmemmap_optimizable_order(pfn_to_section_compound_order(pf= n)) && >>>>>>>>>> + page_zone_id(page + VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES) = !=3D >>>>>>>>>> + page_zone_id(page)); >>>>>>>>>=20 >>>>>>>>> Hmm, page + VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES is = initialized a tad later >>>>>>>>> than page so it'll have stale data in the page->flags, won't = it? >>>>>>>>=20 >>>>>>>> Lance is right. The shared tail struct pages are already = initialized by >>>>>>>> vmemmap_shared_tail_page() during vmemmap population, so = they're not stale. >>>>>>>> The head 64 struct pages are initialized later =E2=80=94 right = here, after vmemmap >>>>>>>> population. >>>>>>>=20 >>>>>>> Still it looks out of place here, can this check be done in = sparse-vmemmap >>>>>>> somehow? >>>>>>=20 >>>>>> The struct page entries of a vmemmap-optimizable compound page >>>>>> are currently initialized in two stages. During vmemmap >>>>>> population, the shared tail entries are initialized first. The >>>>>> retained head area=E2=80=94normally 64=E2=80=94is initialized = later through >>>>>> __init_single_page(). >>>>>>=20 >>>>>> This warning connects the two stages: while initializing the >>>>>> retained entries in the second stage, it verifies that their zone >>>>>> information is consistent with the shared entries initialized in >>>>>> the first stage. Therefore, the same check cannot be performed >>>>>> during vmemmap population. >>>>>>=20 >>>>>> I am planning to first unify the HugeTLB and Device DAX >>>>>> compound-page initialization through a common helper [1]. Once = that >>>>>> work is complete, maybe it will be easy to move the = initialization >>>>>> of the retained head area into vmemmap population. With both the >>>>>> retained and shared entries initialized in the same stage, there >>>>>> will be no cross-stage inconsistency to check, and this warning >>>>>> can be removed. >>>>>>=20 >>>>>> Would keeping the check here for now and removing it as part of >>>>>> that follow-up sound reasonable to you? >>>>>=20 >>>>> While it feels really out of place in __init_single_page(), but = having it >>>>> memmap_init_range() close to the if that skips shared tail pages = makes >>>>> sense. >>>>>=20 >>>>> What do you say? >>>>=20 >>>> Sorry for the late reply because of traveling to LPC. >>>>=20 >>>> Putting the check in memmap_init_range() would validate the >>>> invariant for the shared-tail range skipped there. It would >>>> not, however, cover all vmemmap-optimized initialization >>>> paths: optimized Device DAX bypasses memmap_init_range() >>>> when there is no altmap, and deferred boot-time HugeTLB >>>> initialization may also initialize retained entries >>>> elsewhere. >>>>=20 >>>> If the intention is to validate only the skip in >>>> memmap_init_range(), moving it there makes sense. If we want >>>> the warning to cover both HugeTLB and Device DAX generally, >>>> it still needs to remain in __init_single_page() or be >>>> called from the individual initialization paths. >>>=20 >>> Yeah, putting this into all the callers sucks too :( >>>=20 >>> With all the callers,__init_single_page() is the right place for = this >>> check, but I think we can add a static inline in sparse.h, like e.g. >>>=20 >>> vmemmap_optimization_verify_zone(page, pfn) >>>=20 >>> to make it a bit nicer. >>=20 >> Yeah, factoring this into a helper makes sense. >>=20 >> Since it currently has only one caller, how about keeping it as a = local >> static inline in mm_init.c instead of putting it in sparse.h? >=20 > Presuming we don't expect new callers any time soon let's put it just = above > __init_single_page(). Make sense. Thanks, Muchun >=20 > --=20 > Sincerely yours, > Mike.