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[80.230.25.45]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45d9adc2209sm54072453f8f.0.2026.05.20.15.22.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 May 2026 15:22:41 -0700 (PDT) Date: Wed, 20 May 2026 18:22:36 -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 v8 25/37] mm: page_alloc: clear PG_zeroed on buddy merge if not both zero Message-ID: <68d88e8d227865ec4f8513d47bdbe06d0482851a.1779315441.git.mst@redhat.com> References: 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: X-Mailer: git-send-email 2.27.0.106.g8ac3dc51b1 X-Mutt-Fcc: =sent 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 --- include/linux/page-flags.h | 1 + mm/page_alloc.c | 15 ++++++++++++++- 2 files changed, 15 insertions(+), 1 deletion(-) diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 4ee64134acc3..ff0b192b38e5 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -680,6 +680,7 @@ FOLIO_FLAG_FALSE(idle) * uses this to skip redundant zeroing in post_alloc_hook(). */ __PAGEFLAG(Zeroed, zeroed, PF_NO_COMPOUND) +CLEARPAGEFLAG(Zeroed, zeroed, PF_NO_COMPOUND) #define __PG_ZEROED (1UL << PG_zeroed) /* diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 4cb7e779a6c5..ff614e422eec 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