From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A25BBCD8C9F for ; Mon, 8 Jun 2026 11:47:18 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E20636B0093; Mon, 8 Jun 2026 07:47:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DD1166B0096; Mon, 8 Jun 2026 07:47:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CE6836B0098; Mon, 8 Jun 2026 07:47:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id C18F86B0093 for ; Mon, 8 Jun 2026 07:47:17 -0400 (EDT) Received: from smtpin18.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 7283B1C2A25 for ; Mon, 8 Jun 2026 11:47:17 +0000 (UTC) X-FDA: 84856569714.18.A4E506F Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf29.hostedemail.com (Postfix) with ESMTP id D9FF6120002 for ; Mon, 8 Jun 2026 11:47:15 +0000 (UTC) Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ZSdkhYB+; spf=pass (imf29.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1780919235; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=XYBSlu0D8nqZHl8IsBFYqN57OEwm5p6GA9bMuLV8h3E=; b=Gpm3fuixTE3uhRXIK2yRV9/xGHxYscRJmYuu/mW0xu3mDdWAppaOkDKjs+7ofQADN7sKq5 nTR8Jb+nrUpR36IbKLYaD0GyAdUbw11p2Z3hxmfwuRRfhP6JmClNAGMOViXp2Ov6PyguNl PQr8A4+IxARtwtsE0kKKHUrYA2H4JD0= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ZSdkhYB+; spf=pass (imf29.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1780919235; b=W+0DE+wDJFuq5YnrRJ8UI5l5o/hJZss07/s3wXyRSVZJLay+Xi3PqHz5jEaaAQN/yEHslD ytT5LYfuoI3NV/0xJ5/XtD/pdMpeUqst+GqEYPnmfhb5gttx5lzqGlIN2x6K0fqBICZ6Hq /lrR8cEmSZt9PgYOX87ZSu/a5ZS3T5E= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 5B0346001D; Mon, 8 Jun 2026 11:47:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F3A0B1F00893; Mon, 8 Jun 2026 11:47:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780919235; bh=XYBSlu0D8nqZHl8IsBFYqN57OEwm5p6GA9bMuLV8h3E=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=ZSdkhYB+h5nSqBOocM55VeVktciFWgwSVnAwGDNXjJ6v9AOxi/mcvgqVl0O23Zt9D rI49yCjv1zm3CN4Gt8yWDwuJkyziTaNExRTEew34/k2iNz0/Dv8+3f1+j6f5SSRBbk L8azeh8QnmhqEKzHKSrC86RBNlDkbpegBfN4+Dr+zJJMfk3SsOM+2wdlfgRbHskyTp 88waY2q0XSyxY6uuYjeF3H0vqzXhiw0F2Ebklodbyyu2o2FgT91sRDMGKdcnZMK2us wj8lwU1YosFD65co8DZa7+499Gd9OggnXIN8ObP/f/g37R0tuo2HQRDMwH4wYYGyvd KekWOT4YI8tKQ== Date: Mon, 8 Jun 2026 12:47:01 +0100 From: Lorenzo Stoakes To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, "David Hildenbrand (Arm)" , Jason Wang , Xuan Zhuo , Eugenio =?utf-8?B?UMOpcmV6?= , Muchun Song , Oscar Salvador , Andrew Morton , "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: Re: [PATCH v10 19/37] mm: page_alloc: clear PG_zeroed on buddy merge if not both zero Message-ID: References: <918897302a4cab9f476625adc238ec65a688d1d7.1780906288.git.mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <918897302a4cab9f476625adc238ec65a688d1d7.1780906288.git.mst@redhat.com> X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: D9FF6120002 X-Stat-Signature: j1hazcgdw6teshohw7y99od7qtp3ypie X-Rspam-User: X-HE-Tag: 1780919235-933557 X-HE-Meta: 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 slzOgrqh OpGgT5gVLM/Hvh2f76geSkgk/SPJEsm8pNxduA1h6HpZkA5tvrar7P7tX8QQYGrMezE6jrs1UdkrGow/HtR+szG4o7SENchUEH1GT1gBrNwjTUdaaSL/zYD0KVvZU/bhkuA25GltgRF64HmjvSqXEpDTxrA3Ka9CJ9IW+w3sLVVEps0HBLXMc1vh2Upl95SZxH8crFI6rJBziscwzSEf7TGYLHJaIDIFiykChtjTfunEpUp8rA2J6L44ugld1b/DyvoAtASO7mJWYSuHk8ciakq6L89rqnSZIuujOjWnUqAk0F4l1w4ERGiiCYjBzhJbodt9ZIpWTqwUtYPpAGAJoc6W1PKVZ9c9tZ7krIoESildUEXIvxjgm1jwZa6cJy2xN8ceHZ9Z6ElSCKcJeiezoQFIGdrczF+2mnq7NyuG1/cuwKjqIs2+toZqD8f6DN8Cr4Hp9b6CBj8s5kuI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jun 08, 2026 at 04:38:08AM -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 > 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 91f8ddb1d512..9365d59ac1d6 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 edfc83571985..a90bca5317c1 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -941,10 +941,14 @@ 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 & NIT: We don't add new VM_BUG_ON()'s, please use VM_WARN_ON(). > + (PAGE_FLAGS_CHECK_AT_PREP & ~__PG_ZEROED), page); > > VM_BUG_ON(migratetype == -1); > VM_BUG_ON_PAGE(pfn & ((1 << order) - 1), page); > @@ -979,6 +983,8 @@ 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. > @@ -997,10 +1003,17 @@ 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 >