From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-24.mta1.migadu.com [95.215.58.24]) (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 5E5003C1992 for ; Mon, 5 Oct 2026 16:28:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.24 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791217689; cv=none; b=AyySQtPPGFffvsmiwBeIrLa2k1BnsVr2TpZ0szErJrtFYXYSPnBj7bufWdL92rKJ4VEPg2pzgQRUoFdlOWdRpELUi5qpv2nUEprYR3/MbxdNbJvzx+RGZwytNTZKakN6HR8WkScwSi0YbLq45LRDlNYrKVVW0x8UlEZg1oEsLQw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791217689; c=relaxed/simple; bh=9+Tmnole7q0+tJ56UU4LkJKNC6EUiAUTbjpFGb9K7q4=; h=Content-Type:Mime-Version:Subject:From:In-Reply-To:Date:Cc: Message-Id:References:To; b=Fy9RLOzu3RlDEyVjJOclo6md3kc/5srtsGRcK7kLyddAeEGuAli2D0R8mYwPaTzg47gXVCEhWE4HN7+fICDY3VFT5WeaebcyS3wbWua+Cr/UokP6NhJTzUYb7+lqzEP0p5vrHoIup7uA+wuAo983ESZGUSoqloV3Yf6oFI5/uTE= 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=kl5Mb8yq; arc=none smtp.client-ip=95.215.58.24 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="kl5Mb8yq" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=9+Tmnole7q0+tJ56UU4LkJKNC6EUiAUTbjpFGb9K7q4=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1791217685; v=1; x=1791822485; b=kl5Mb8yqAuBa1ysN4KRQ/JRXmdxeVWgpzqucHYaDFiWSuE1w7xoNqVIahcjpYYtcpmdvXvuQ z35vK9O03ciH2ppTch+uh8c6aUlBdcdWtI4eKsFBFDBA+lwCvzrfVvnJLg7jd5IIVVxrDw0T4hs FHVSGsQ3NMaX0drJVlCzGlfQ= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id fa22e0d45fa7ff67; Mon, 05 Oct 2026 16:28:04 +0000 X-Mizu-Trace-ID: fa22e0d45fa7ff67 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: Mon, 5 Oct 2026 18:27:52 +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: 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 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? Sorry for the late reply because of traveling to LPC. 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. 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. Thanks, Muchun >=20 >> [1] = https://lore.kernel.org/20260513132044.41690-18-songmuchun@bytedance.com/ >>=20 >> Thanks, >> Muchun >=20 > --=20 > Sincerely yours, > Mike.