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[2003:d8:2f26:ba00:803:6ec5:9918:6fd]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-3c077788b39sm12802789f8f.47.2025.08.21.13.07.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 21 Aug 2025 13:07:34 -0700 (PDT) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: David Hildenbrand , 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 , Mike Rapoport , 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: [PATCH RFC 10/35] mm/hugetlb: cleanup hugetlb_folio_init_tail_vmemmap() Date: Thu, 21 Aug 2025 22:06:36 +0200 Message-ID: <20250821200701.1329277-11-david@redhat.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250821200701.1329277-1-david@redhat.com> References: <20250821200701.1329277-1-david@redhat.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: IPuh84AozdrXoVRaLowBYHhzxamk7DEKh7WZ-HlbwEw_1755806855 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true All pages were already initialized and set to PageReserved() with a refcount of 1 by MM init code. In fact, by using __init_single_page(), we will be setting the refcount to 1 just to freeze it again immediately afterwards. So drop the __init_single_page() and use __ClearPageReserved() instead. Adjust the comments to highlight that we are dealing with an open-coded prep_compound_page() variant. Further, as we can now safely iterate over all pages in a folio, let's avoid the page-pfn dance and just iterate the pages directly. 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 | 21 ++++++++++----------- 1 file changed, 10 insertions(+), 11 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index d12a9d5146af4..ae82a845b14ad 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3235,17 +3235,14 @@ static void __init hugetlb_folio_init_tail_vmemmap(struct folio *folio, unsigned long start_page_number, unsigned long end_page_number) { - enum zone_type zone = zone_idx(folio_zone(folio)); - int nid = folio_nid(folio); - unsigned long head_pfn = folio_pfn(folio); - unsigned long pfn, end_pfn = head_pfn + end_page_number; + struct page *head_page = folio_page(folio, 0); + struct page *page = folio_page(folio, start_page_number); + unsigned long i; int ret; - for (pfn = head_pfn + start_page_number; pfn < end_pfn; pfn++) { - struct page *page = pfn_to_page(pfn); - - __init_single_page(page, pfn, zone, nid); - prep_compound_tail((struct page *)folio, pfn - head_pfn); + for (i = start_page_number; i < end_page_number; i++, page++) { + __ClearPageReserved(page); + prep_compound_tail(head_page, i); ret = page_ref_freeze(page, 1); VM_BUG_ON(!ret); } @@ -3257,12 +3254,14 @@ 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 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