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[80.230.48.7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48e53907e8asm148617135e9.13.2026.05.07.15.23.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 07 May 2026 15:23:21 -0700 (PDT) Date: Thu, 7 May 2026 18:23:19 -0400 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , linux-mm@kvack.org Subject: [PATCH v5 18/28] mm: page_alloc: clear PG_zeroed on buddy merge if not both zero Message-ID: <9928bb52244928b53172e7d95f770bc63d982b4e.1778192416.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 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 e5db2601d673..63b7f396ff30 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -984,10 +984,14 @@ 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); @@ -1022,6 +1026,8 @@ 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. @@ -1040,10 +1046,17 @@ 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