From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 E47243F0A81 for ; Thu, 8 Oct 2026 07:45:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791445546; cv=none; b=OLOuGiezTNAkVwA+tnk5lz+Su2OM13SD+y8S5dZJs7fahKTcCBYcsQrzTXKKEMctehwgADWaYuAuxWslvwe85Znjpzz1vCBVdHSkhUgZ64xs8pDs2gxAsf5LfJD/futP460ukYrtz1MoLE09jHKshFDWYZ4dEai6FNENIp+4hSg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791445546; c=relaxed/simple; bh=X4b1asA38Pu+GIKjArxkkSIUclUvQzzIH54CvGfiGgw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=K+ihMU99GIyNfjGD1Av1qSGCbQJEZO53DTpVgqxhp7RaBky//tYypZkELjdwBq4S03ns0wT0Ktqrw6BC3o47cNrMMLiUf8roL8pKcWnnkEUhtkAAJqx0sLLacj/nYrgQawuC0vSblJkYFvzkG7wbcrpmzgm12bNRuszRgu6RBk4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=efbSkEJ2; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="efbSkEJ2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 80CE81F00893; Thu, 8 Oct 2026 07:45:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791445544; bh=Y82KYwy06rNpAA7M8MsmLg3p1srKgmRdrrUbRlrqajQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=efbSkEJ2rpc8pzH1kPR2J923tKrUfBE7MQ7w+c75c9zz7kP1udsRu2q9egp9bcVVb yex1rX8rZYHKwIlwUyH2D2Nfd7iXsk6ngLByQ5EeiA/VKWQkHNdXr8/pXHIKH0dF7e emoGLzk9iEzmtV9p95S1RT0gfKJWTc7J3Dgx36p8pUvMlNWbOldrTtDeHL3Yv4cV6X AAFv3A5HqO2wgDoihb0FNE4EngPcehF9Tar+Xv/l2XFB9bLf8yaK76ERBqLZmgDALH jop9A4VdvQ42FDAVIQQXT2hSlZQaTyJEtnunTHbyiGbEObu/a3PDj2b/kuWjWl/j+Z c1Oo6pn9hqBsw== Date: Thu, 8 Oct 2026 09:45:35 +0200 From: Mike Rapoport To: Muchun Song 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 Subject: Re: [PATCH v3 6/6] mm/mm_init: add zone mismatch warning during page init 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Oct 06, 2026 at 03:32:43PM +0200, Muchun Song wrote: > > On Oct 6, 2026, at 12:52, Mike Rapoport wrote: > > > > On Mon, Oct 05, 2026 at 06:27:52PM +0200, Muchun Song wrote: > >>> On Oct 2, 2026, at 20:12, Mike Rapoport wrote: > >>> > >>> On Fri, Oct 02, 2026 at 05:56:40PM +0800, Muchun Song wrote: > >>>>> On Oct 2, 2026, at 16:22, Mike Rapoport wrote: > >>>> > >>>>>>>> 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(pfn)) && > >>>>>>>> + page_zone_id(page + VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES) != > >>>>>>>> + page_zone_id(page)); > >>>>>>> > >>>>>>> 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? > >>>>>> > >>>>>> 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 — right here, after vmemmap > >>>>>> population. > >>>>> > >>>>> Still it looks out of place here, can this check be done in sparse-vmemmap > >>>>> somehow? > >>>> > >>>> 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—normally 64—is initialized later through > >>>> __init_single_page(). > >>>> > >>>> 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. > >>>> > >>>> 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. > >>>> > >>>> Would keeping the check here for now and removing it as part of > >>>> that follow-up sound reasonable to you? > >>> > >>> 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. > >>> > >>> 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. > > > > Yeah, putting this into all the callers sucks too :( > > > > 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. > > > > vmemmap_optimization_verify_zone(page, pfn) > > > > to make it a bit nicer. > > Yeah, factoring this into a helper makes sense. > > 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? Presuming we don't expect new callers any time soon let's put it just above __init_single_page(). -- Sincerely yours, Mike.