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[80.230.48.7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48e8f4247fasm29156585e9.9.2026.05.12.08.58.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 May 2026 08:58:32 -0700 (PDT) Date: Tue, 12 May 2026 11:58:27 -0400 From: "Michael S. Tsirkin" To: Gregory Price Cc: linux-kernel@vger.kernel.org, "David Hildenbrand (Arm)" , Jason Wang , Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , 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 , 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: Re: [PATCH resend v6 20/30] mm: page_alloc: clear PG_zeroed on buddy merge if not both zero Message-ID: <20260512115805-mutt-send-email-mst@kernel.org> References: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: prP_jTJwmVA1elWOwfhjWmgwpISz7oiKYk9BqfxTLuI_1778601514 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 14350C0007 X-Stat-Signature: k1mi4h3knk766f7q1rxpaki65tf5zy4j X-HE-Tag: 1778601516-644600 X-HE-Meta: U2FsdGVkX1/BQSEJyX2aoE94ynMOlfbKYm9+rTdqlQA49tcM4GkIueyj1WYnT+fJM6xe4gaa3n5/iBmrYYboFY9yEP6O4/jkuoQLgHQ3BqZGTRltSCMf/Dkye3DoPSOYUq2S/iZXbd2KCJI7RPZo0sHgVtIw/j4SnIKUrxj0PhpSJa+C4MdA7fdUBZDfSaOWusYal/DpFP5aygH4JyQ1VP2Oh9Xvvxn3qMl8ujqtnVuehsG42hIJhJj0gf3o0fW38PaOnHlP2TNKtgiNtUsOhuQ7XdGClcSOYeBolBSsvLO3aRU/ZWyvMctGg0qFYOtFaJiO6pFTiC+DcD2SRjmxgQzXLy8ZweTB9Zyjag5ZIoQlTenNtT2zWTmDWZ2MH/6k/AD7XlsC1MysHKmtCHNi47ce1QVD01n57wGk/X1ikxgyuR11wjcFyDvdNIto0WnZaZGWcXQdOo9Tx0GqJIHN+W3RVSJolfhlttq5QeJx98dy+8E8lJI7qwsj+vuAMVOERkm8T2MqBm3AVpptyOmr9JCX1QyY/E2EYT6n6kf1f9FOx3GwpTO17pD5hYn/4uFQLEIJ3qt8QBdY6kwUswHp6W29UFwYEkt917i/sSrPT5RW92+g7jfjwtqvX4yLNRhO2Lup1SZd1stg1TpPuwf6/WSYj/sZz2Rlfu55D5O5TiQcd8WWahuVva5CepquaChniseDHDpd8pEk60xUY7u9bshD1bC7l0lrQMgd0XwmjIjseQngrI1kdbWWvaMMJMo8bfBE2/3NwPCiustm6h8xvHgnthSB8Sj/8PYK3Ud+LDp35GIKPvHJfs0l4BSFjW5uIeTkmN9et1hBE4mENU4ocZdeb2nXiu/iH2oyIKOeXyy+kTu7/ZNZHpDhC+fWT9zJkwBDcfQD87e4pNEMMMpAehZMGUgRO1b1RtAWF16u9kcWmxQ9V7HEmtHA8+YpJ1ssr3z1PHZiEwAuUlPGPUn afL4AN8Q tZcNOI4Zbu944jr1yxI42rRg1ClKdWIjkvP8cBvlnoaJlMYh8ECtFZqsLhte1pXjCplcHLca1gk6KB11FrpM6AVkUAOA70gHk8XIgaZo3FkGPDGKqjDiezruq38xBMa3F0PFxrnP7r2f1Tr+vDXkaMn0mA8wWYeyxc8VshtrajK3m7ESznGLrDemMEARQK75ApcGsgjelK8cg2BM0xXpmBOdG4h6rd/6+R09NRLfgdiOGbAlvL0nzJOCIpjQpGHYeq7wA8U3fdpTScscJQlhGWsayxeymVCIcxYvAczYlmFilTNQFUX7ZcTfF9VLuSZ88UpczG/aM3vS+2ZBYoBPso/5HBzozv7vfjdSdj4OIphgJg/ixHOGH+3rlME8zkGIZbkMBpQ1amOugMTQUbUJ1WK1Ni57l13RNi0DgqX/+kGB04MUPu78C8GeiJQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, May 12, 2026 at 11:56:02AM -0400, Gregory Price wrote: > On Mon, May 11, 2026 at 05:03:35AM -0400, Michael S. Tsirkin wrote: > > 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 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; > > If you want to play some code golf, i think you can get away with a > single bool here: > > bool zeroed; > zeroed = PageZeroed(buddy); > zeroed &= PageZeroed(page); > > if (zeroed) > __SetPageZeroed(page); > > ~Gregory Does it matter? It makes my head hurt. -- MST