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 7159D3ACF10 for ; Mon, 13 Apr 2026 09:35:22 +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=1776072922; cv=none; b=QArkV/av+GzR1XDh/uCMfFJBSxLpK5GmIijKKcY2UwtA9v3CLKAVr62zfTViKVJPJrur3Znz7VVI5OWSPp9fAUzglrn/yWHD3DZup3/g9SD5DE5En+FWDrQeAKSt1gCRJfqMbWhgZJajoGHLuUimU9831+s4F3hDbWgx2LK/MeU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776072922; c=relaxed/simple; bh=K0G+OC7cY44wL3XcPEIszFCe8WkP7B+tqb8dxqmAp5Q=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NgdKs0qfYf0GtiSZ4FvDrlXpU8RSFYaJFExWA4o84nnQ7OdViKyzPRGtipsRGt1j5+1Pep1AAtV2U241qRUNoAfp4osnRj3rtTEbNoDbf8qMGhMotkiHDJp1aaDA7TowtvWEzU+CBySm9NKo2fD3YlNJEPQQraVUMoCvwKWW9Fw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=b715bc9u; 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="b715bc9u" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4C7F8C2BCAF; Mon, 13 Apr 2026 09:35:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776072922; bh=K0G+OC7cY44wL3XcPEIszFCe8WkP7B+tqb8dxqmAp5Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=b715bc9uzu+xDII7oSF3dk+qOb9Vy5kUF5WF9SZfGz2uUH5z4NP3CDsqIEMMddhYl jxoIm1krczDBDHzTrZ8sq9L6EB7Kj3MunIE/1BZkIGy32ct9v6rhIhS1/19UuaqNg/ oZSbWBMPwojj5BDvW452xa6g1N+CJPZz2GqXarzFOG8oC3HIt913VTcVEi2Qn1HlO/ Gpv2w6oL7N7pmOn0pxC/E6tJNwY5SdVaGvyQs7z/ZZ7sW0ncwMSqrBuXZ3VjbjCCTj QU1VAlcKKugE6apzNGFx0ZaNhz89VrBiv445k93tg26DA8flS5AOnZrZdQFboJd+ti 3ihwJIH1ISmoQ== Date: Mon, 13 Apr 2026 12:35:12 +0300 From: Mike Rapoport To: Muchun Song Cc: Andrew Morton , David Hildenbrand , Muchun Song , Oscar Salvador , Michael Ellerman , Madhavan Srinivasan , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Nicholas Piggin , Christophe Leroy , aneesh.kumar@linux.ibm.com, joao.m.martins@oracle.com, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 01/49] mm/sparse: fix vmemmap accounting imbalance on memory hotplug error Message-ID: References: <20260405125240.2558577-1-songmuchun@bytedance.com> <20260405125240.2558577-2-songmuchun@bytedance.com> 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=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Apr 13, 2026 at 12:19:50PM +0300, Mike Rapoport wrote: > On Sun, Apr 05, 2026 at 08:51:52PM +0800, Muchun Song wrote: > > In section_activate(), if populate_section_memmap() fails, the error > > handling path calls section_deactivate() to roll back the state. This > > approach introduces an accounting imbalance. > > > > Since the commit c3576889d87b ("mm: fix accounting of memmap pages"), > > memmap pages are accounted for only after populate_section_memmap() > > succeeds. However, section_deactivate() unconditionally decrements the > > vmemmap account. Consequently, a failure in populate_section_memmap() > > leads to a negative offset (underflow) in the system's vmemmap tracking. > > > > We can fix this by ensuring that the vmemmap accounting is incremented > > immediately before checking for the success of populate_section_memmap(). > > If populate_section_memmap() fails, the subsequent call to > > section_deactivate() will decrement the accounting, perfectly offsetting > > the increment and maintaining balance. > > > > Fixes: c3576889d87b ("mm: fix accounting of memmap pages") > > Signed-off-by: Muchun Song > > --- > > mm/sparse-vmemmap.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c > > index 6eadb9d116e4..ee27d0c0efe2 100644 > > --- a/mm/sparse-vmemmap.c > > +++ b/mm/sparse-vmemmap.c > > @@ -822,11 +822,11 @@ static struct page * __meminit section_activate(int nid, unsigned long pfn, > > return pfn_to_page(pfn); > > > > memmap = populate_section_memmap(pfn, nr_pages, nid, altmap, pgmap); > > + memmap_pages_add(DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE)); > > This logically belongs to success path in populate_section_memmap(). If we > update the counter there, we won't need to temporarily increase it at all. Not strictly related to this patchset, but it seems, we can have a single memmap_boot_pages_add() in memmap_alloc() rather than to update the counter in memmap_alloc() callers. > > if (!memmap) { > > section_deactivate(pfn, nr_pages, altmap); > > return ERR_PTR(-ENOMEM); > > } > > - memmap_pages_add(DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE)); > > > > return memmap; > > } > > -- > > 2.20.1 > > > > -- > Sincerely yours, > Mike. -- Sincerely yours, Mike.