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[80.230.48.7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48e8f42a845sm24872145e9.20.2026.05.12.14.06.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 May 2026 14:07:03 -0700 (PDT) Date: Tue, 12 May 2026 17:06:59 -0400 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: "David Hildenbrand (Arm)" , Jason Wang , Xuan Zhuo , Eugenio =?utf-8?B?UMOpcmV6?= , Muchun Song , Oscar Salvador , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Hugh Dickins , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Axel Rasmussen , Yuanchu Xie , Wei Xu , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , virtualization@lists.linux.dev, linux-mm@kvack.org, Andrea Arcangeli Subject: [PATCH v7 21/31] mm: page_alloc: clear PG_zeroed on buddy merge if not both zero Message-ID: References: MIME-Version: 1.0 In-Reply-To: X-Mailer: git-send-email 2.27.0.106.g8ac3dc51b1 X-Mutt-Fcc: =sent X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Mwke1zzU8EqgBiUBq0Pi7u2FU1zJPq5xdVoasNrNDLQ_1778620026 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: AC8C140006 X-Stat-Signature: w7jf11huf87gfs6ynnsj5qynh47p1wcx X-Rspam-User: X-HE-Tag: 1778620031-466236 X-HE-Meta: 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 c1Fi2325 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: When two buddy pages merge in __free_one_page(), preserve PG_zeroed on the merged page only if both buddies have the flag set. Otherwise clear it. The merged page would inherit PG_zeroed, and a later __GFP_ZERO allocation would skip zeroing stale data in the non-zero half. Signed-off-by: Michael S. Tsirkin Reviewed-by: Gregory Price Assisted-by: Claude:claude-opus-4-6 Assisted-by: cursor-agent:GPT-5.4-xhigh --- mm/page_alloc.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index bd3b909cacdf..d70c9ba6b329 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -940,10 +940,14 @@ static inline void __free_one_page(struct page *page, unsigned long buddy_pfn = 0; unsigned long combined_pfn; struct page *buddy; + bool buddy_zeroed; + bool page_zeroed; bool to_tail; VM_BUG_ON(!zone_is_initialized(zone)); - VM_BUG_ON_PAGE(page->flags.f & PAGE_FLAGS_CHECK_AT_PREP, page); + /* PG_zeroed (aliased to PG_private) is valid on free-list pages */ + VM_BUG_ON_PAGE(page->flags.f & + (PAGE_FLAGS_CHECK_AT_PREP & ~__PG_ZEROED), page); VM_BUG_ON(migratetype == -1); VM_BUG_ON_PAGE(pfn & ((1 << order) - 1), page); @@ -978,6 +982,8 @@ static inline void __free_one_page(struct page *page, goto done_merging; } + buddy_zeroed = PageZeroed(buddy); + /* * Our buddy is free or it is CONFIG_DEBUG_PAGEALLOC guard page, * merge with it and move up one order. @@ -996,10 +1002,17 @@ static inline void __free_one_page(struct page *page, change_pageblock_range(buddy, order, migratetype); } + page_zeroed = PageZeroed(page); + __ClearPageZeroed(page); + __ClearPageZeroed(buddy); + combined_pfn = buddy_pfn & pfn; page = page + (combined_pfn - pfn); pfn = combined_pfn; order++; + + if (page_zeroed && buddy_zeroed) + __SetPageZeroed(page); } done_merging: -- MST