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 5D8C31C861E; Thu, 28 Aug 2025 07:21:19 +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=1756365680; cv=none; b=e406n6xlgoh44vowxDAyKhpzgPDQOs2aQGmBfj9Qq+LBnj9Pam1CqYJk7HTaUYSS1/61wspdiSTpKETjXOA25hZiu6giedIBevF9lO87JlO/E47Ocf0sTWqu3Kg8cnbUCVa4P19H2kEakjS6vYQ6lIfz4Q14lpfoxttV9IlYIpM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756365680; c=relaxed/simple; bh=C7/duUHB1jzTe2zoRwJGPq9tnOYsk04M/lnKM6Lw4jw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XWXxilYOr7zfaFxfaG8BqduxMte0OHv5QZf2jAu6qSzCbEEgYtuVyetgDcLIVH5glDbYOZMWK+XOUqOzP89eN2TP8GwZFeWA35U+LkO8yW/M2O47u3YUcZKRE1zsilhvtkhr6bxznz9BTSKXj7DguWS5MXaw0RMQuKse7Bre6Bg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=P3P6rik2; 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="P3P6rik2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D6A4FC4CEF5; Thu, 28 Aug 2025 07:21:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1756365679; bh=C7/duUHB1jzTe2zoRwJGPq9tnOYsk04M/lnKM6Lw4jw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=P3P6rik2V+dAnat9eWuSvAQFs7ROQol0qfl7mXX/2cUYI+C7QRP3XNCAjTFTXOboX PnGh4LwLXGdtC/lBzkP3HHTgLg4rsEUWyyc9GJT6llTjHe+2h8KOlurSZnUiJw3NW7 qKwPWdsXnTrtZmXRScitgLnU7lvFVln3pfXq+R+VNtWe5rSbPPMi2iORZuC/qKAp5S 3fe04bSwMQR8OaSYcElHlHSfQVwB6Zb3HSUqkl5IfcwdDCl1ZwfSrzEWyOB1KGcrlw JUhlVcCM4Av5WDpYuP6k5h/vdvl0/1bLz8dvd0y2eUBSbWa12OIyuKGJ2VR5zTU1an L77vfQGsfA4Og== Date: Thu, 28 Aug 2025 10:21:00 +0300 From: Mike Rapoport To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, Alexander Potapenko , Andrew Morton , Brendan Jackman , Christoph Lameter , Dennis Zhou , Dmitry Vyukov , dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, iommu@lists.linux.dev, io-uring@vger.kernel.org, Jason Gunthorpe , Jens Axboe , Johannes Weiner , John Hubbard , kasan-dev@googlegroups.com, kvm@vger.kernel.org, "Liam R. Howlett" , Linus Torvalds , linux-arm-kernel@axis.com, linux-arm-kernel@lists.infradead.org, linux-crypto@vger.kernel.org, linux-ide@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mips@vger.kernel.org, linux-mmc@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, Lorenzo Stoakes , Marco Elver , Marek Szyprowski , Michal Hocko , Muchun Song , netdev@vger.kernel.org, Oscar Salvador , Peter Xu , Robin Murphy , Suren Baghdasaryan , Tejun Heo , virtualization@lists.linux.dev, Vlastimil Babka , wireguard@lists.zx2c4.com, x86@kernel.org, Zi Yan Subject: Re: [PATCH v1 13/36] mm/hugetlb: cleanup hugetlb_folio_init_tail_vmemmap() Message-ID: References: <20250827220141.262669-1-david@redhat.com> <20250827220141.262669-14-david@redhat.com> Precedence: bulk X-Mailing-List: linux-s390@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: <20250827220141.262669-14-david@redhat.com> On Thu, Aug 28, 2025 at 12:01:17AM +0200, David Hildenbrand wrote: > We can now safely iterate over all pages in a folio, so no need for the > pfn_to_page(). > > Also, as we already force the refcount in __init_single_page() to 1, > we can just set the refcount to 0 and avoid page_ref_freeze() + > VM_BUG_ON. Likely, in the future, we would just want to tell > __init_single_page() to which value to initialize the refcount. > > Further, adjust the comments to highlight that we are dealing with an > open-coded prep_compound_page() variant, and add another comment explaining > why we really need the __init_single_page() only on the tail pages. > > Note that the current code was likely problematic, but we never ran into > it: prep_compound_tail() would have been called with an offset that might > exceed a memory section, and prep_compound_tail() would have simply > added that offset to the page pointer -- which would not have done the > right thing on sparsemem without vmemmap. > > Signed-off-by: David Hildenbrand > --- > mm/hugetlb.c | 20 ++++++++++++-------- > 1 file changed, 12 insertions(+), 8 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 4a97e4f14c0dc..1f42186a85ea4 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -3237,17 +3237,18 @@ static void __init hugetlb_folio_init_tail_vmemmap(struct folio *folio, > { > enum zone_type zone = zone_idx(folio_zone(folio)); > int nid = folio_nid(folio); > + struct page *page = folio_page(folio, start_page_number); > unsigned long head_pfn = folio_pfn(folio); > unsigned long pfn, end_pfn = head_pfn + end_page_number; > - int ret; > - > - for (pfn = head_pfn + start_page_number; pfn < end_pfn; pfn++) { > - struct page *page = pfn_to_page(pfn); > > + /* > + * We mark all tail pages with memblock_reserved_mark_noinit(), > + * so these pages are completely uninitialized. ^ not? ;-) > + */ > + for (pfn = head_pfn + start_page_number; pfn < end_pfn; page++, pfn++) { > __init_single_page(page, pfn, zone, nid); > prep_compound_tail((struct page *)folio, pfn - head_pfn); > - ret = page_ref_freeze(page, 1); > - VM_BUG_ON(!ret); > + set_page_count(page, 0); > } > } > > @@ -3257,12 +3258,15 @@ static void __init hugetlb_folio_init_vmemmap(struct folio *folio, > { > int ret; > > - /* Prepare folio head */ > + /* > + * This is an open-coded prep_compound_page() whereby we avoid > + * walking pages twice by initializing/preparing+freezing them in the > + * same go. > + */ > __folio_clear_reserved(folio); > __folio_set_head(folio); > ret = folio_ref_freeze(folio, 1); > VM_BUG_ON(!ret); > - /* Initialize the necessary tail struct pages */ > hugetlb_folio_init_tail_vmemmap(folio, 1, nr_pages); > prep_compound_head((struct page *)folio, huge_page_order(h)); > } > -- > 2.50.1 > -- Sincerely yours, Mike.