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 9BEE6CD37AC for ; Thu, 7 May 2026 22:23:28 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B10BA6B00D5; Thu, 7 May 2026 18:23:27 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id AE8C36B00D7; Thu, 7 May 2026 18:23:27 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9D8056B00D8; Thu, 7 May 2026 18:23:27 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 680AE6B00D5 for ; Thu, 7 May 2026 18:23:27 -0400 (EDT) Received: from smtpin04.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 2CD8A12065D for ; Thu, 7 May 2026 22:23:27 +0000 (UTC) X-FDA: 84742051254.04.CF4BE15 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf26.hostedemail.com (Postfix) with ESMTP id EE96714000F for ; Thu, 7 May 2026 22:23:24 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=TBACxlXz; spf=pass (imf26.hostedemail.com: domain of mst@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=mst@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1778192605; 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=/cazEjjhaO5BxPm4JyLG8Gc9L6oe2zaOenErLTI/evM=; b=cy/K/0E4k/yyoEPQLXYCc9m0M/Tcr26mOx/VU8QzO6yifUj8mMjDQj0S8vCJosC0IPz6qF eaQjHkOkKfG2YPoK9AT3DO6LgoU5JjcJWvdJxn0tqBtObObkjAOoT6LmxQTFo9x9WII48l fyVzV45+giTigdF5+RRTrOK9gkCHn9g= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=TBACxlXz; spf=pass (imf26.hostedemail.com: domain of mst@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=mst@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1778192605; a=rsa-sha256; cv=none; b=0s1Q5D87orOZ9EpMIK7+ylvGfxBzLVqj3EtZcqc5AoGhpE4+F1M33lttjcswzWtFed9RQs S55Bd6trXmHpwP0Hi1sX36bjAndqKp66qw4qoENPVVFijyBSdJenBdr2sh4PBWao9uNFJI 95hP9lt4GYPD7j1VOmf2xWvwXEIuKIQ= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1778192604; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=/cazEjjhaO5BxPm4JyLG8Gc9L6oe2zaOenErLTI/evM=; b=TBACxlXzaD2DmduvpS/H/KcZgHuUgt9Irgho+YOyoJsIrST4KRcodIoRG1h9BvYerAqGTa Hh3usivjXeMw4xJfVCoidZaixwWlBAwZLpbDQK9sYCYky/NxE+dLd5dG1puShmxN71aa8l /TNSo9fx94Zx58o4D0oym/XnQD8svSM= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-652-0-0n8US-M8m7LaIJ_-ZeXA-1; Thu, 07 May 2026 18:23:23 -0400 X-MC-Unique: 0-0n8US-M8m7LaIJ_-ZeXA-1 X-Mimecast-MFC-AGG-ID: 0-0n8US-M8m7LaIJ_-ZeXA_1778192602 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-48a588ff84eso10591285e9.1 for ; Thu, 07 May 2026 15:23:23 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1778192602; x=1778797402; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=/cazEjjhaO5BxPm4JyLG8Gc9L6oe2zaOenErLTI/evM=; b=NLR1/f3EhHzSllrnBsdJVhngQxziJ4HLSyyye+TK60yCxY8fpkoXAHcrSe5CkbzaoX snXGUahrdxWLUHRRPoUXVXiEzh2F0jjcB8xngIZ9EIdz9u6NmfdPu6Rd1Hrd2fTjxqOD 57GW9tOEu8AE6MlfelKK9uxqtB+cCIqzmjoDKKB8xKZ87gGcv6fvDPLzw/SvegD7qPiv NXTzTeX2NJtJUUjrPHe1mk/JTd7x+HQNqGqI+rChYHqrrX0GvVsTUCVcscnB+WPfHnup Mqjk4q9ulZTW9oyvy6I0+TQCgK/pWxC6lSIO5hOu5G85LizY6oqtH4S4/rHbY3h9bkzL Cq3g== X-Forwarded-Encrypted: i=1; AFNElJ+yeOPX8tS4Jue6MjquX4dwdkUK2EKaO43NCp0jCyL56AwycC4POD37jnR8NcSvPi/r1Q4Y899orQ==@kvack.org X-Gm-Message-State: AOJu0YztI7jX0U8jJ4JClBxJ19S8HGnTDiSb2QoBnE9jGdtvl40OAVqg I77qxDyRhRROGW+A9Yy1VId3+mfKRXUn/EvApy6YPen3bHGF1+RsN4VV40GCVsGb0Y4Hne4A8dY ibHlB+28AZnf3kasO9Y5L4p72mVt1nEV1OlMkXk6j9q3T1kmlxrY9 X-Gm-Gg: AeBDieuedjkZBI5b8CWrEGDu/fnU13Na4bqzePBwmY8cOyzb84X+mernLP+XXKyoDNh KXLD21mI3JLLIGT3N0H4cT66LHEmCcX2vdD2pylIbt58i+j2UJhTD7cfm0tBnao4Qp3ukZimR/v n3MCP8ZUYRzV2VhWrXB9W2yV1np+VFcniVFmQsBLsiRoI1LnX1QIddc8KEA3uE09sm+sflauVw8 y3Abvm0SbE/Yv2Dpz+O1PEjaE49i3AjEqUl9dUpysa9RSkMFZ6A6W7/KaJY0A+8UiWNnDF+JMX8 nbwp/EGddsCzHWpATOD0fvMqZHUpsD+kjgS0GuNyTvncJROCd09LjbuuiLtvqd062EC/DAICuG3 44g0jHpxSnYnBT+5N4L4al3d+HOOmfKRSXerEurWn X-Received: by 2002:a05:600c:4e0c:b0:48d:46a:6e5b with SMTP id 5b1f17b1804b1-48e51e19110mr170280145e9.7.1778192601893; Thu, 07 May 2026 15:23:21 -0700 (PDT) X-Received: by 2002:a05:600c:4e0c:b0:48d:46a:6e5b with SMTP id 5b1f17b1804b1-48e51e19110mr170279835e9.7.1778192601462; Thu, 07 May 2026 15:23:21 -0700 (PDT) Received: from redhat.com (IGLD-80-230-48-7.inter.net.il. [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: 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: bUTA_KtXEaiD8mp2SW1zsg06oOK3l9LJOu7feYQYips_1778192602 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: EE96714000F X-Stat-Signature: igjdknfw9x3oaref9ginnyri3k5oerrm X-HE-Tag: 1778192604-965017 X-HE-Meta: U2FsdGVkX19En8HNLuLb7nBhcWvFG2vpCh0jzthdKXNRVwtNaVju+2+AH0z+VDo87c1B2FkGOWZCVpMqFainCnLvyAOhyWGvIHONa6FLxFhMxJcWPlL76rHvBNTPUwlMT1WJ2e3F2hT0hEcicXChwfpLZWI56IHFY3fwssyLjpzi+IqPl8g/+bXa3bETgOhUTy5emNO7zDlnPjXxbaQEgVXAKLFkH3nVkAPfptIbi8bCe+1RrkqI2qIZcDiPMqUEA0OsAHOLcL3MJjpFXqnTSJ05SRVCN2QztZx8KPoNwMbB7og6zrhE+6f/H0ztHzAX42kMX0dGzeObrLL3M2vqsZF79xcd5h/PAlKsKywskiygk3D7nbwqpbJVVspuIXtoXpQCpqJQa8AI/9aywkxjsbkDtmVb0fKsbXazCEoGLVWYpwSKrvaY/n9azDnbQ0DgJIxuMi1snTfepmFliYsOrIajj+cXo8N6Ax8irwoRKeajjSupLXOKJUp1A+aSXJiBofA3Ea9zayVSjgTQbKTIMHFPVenfcU7bGU0v8s6bjZzr5ET39bdBE5TtfqlqzTcWYy3/9A7HNqKZgPY5HFi4SSgUzJdFTWwEtGoJwKK7hYLZ/PWxkQu5N1IShcI9/xT9m11onWcXw9AYXCEz7WYqEWa4ijL9HtHxYTq85On+K24I60nUMugRIjBTvlASywpgaJlYG5LFQOOeDoZ7BgCxQRg0w/jztiT6Ldpo6ch5L2oFStYk9ssCLWUQurtjyS0nR/HGAZMGx141Zq+Td4C8FcknRR7wooHjjQJSCGBYiBs/lRVtBT3YnCFMuCZFrmiId/ZVQnfc9bCbLqx3FeJEQkMkv29KbmpUUA6uIgx9EWPiXWvlG9u6f/mEgregLqU7VMPS87PoM7P+SnHy91p+zkRVHL4WAYiPWqFK8HhnZMEhX8Nu8BIL4+ttsE9oKksttkYRAykOmbZ3dvtO3C8 sUkfhdfo ePms9Uw7G8kzXjxr9VCSiQVSQazS4UyLicmg2v3U4E/KbjTt8rK6Y7MWI4MFeae4w/OFEpH5Vka3tsAnYGqY9UJy9dchcarCb6nk9xZ68uT7eSXTUDRLCf9xffO7ZkP81wcn/U8dJnswO0dLoeRGGbYcqLUzgwnpWzkzgdNBd4f8BBU2gbA+1OGRH5cP82NMl336cEs/4KvWBiCrRWEzNL6EBNGL83ct8n1N9gfShcX0gvm4yTPRoNHw9AdHWXg4FURmqWa92sQF0eVTpD7icu+ZU6U7W9HiaCe54u0lIZmgcPi+W1lp/cOlpyez0apvMW1wObHve81bovDFinE4U5FPGuARY/P8/JBkrD2uqzAo/09AG0TSMw+53Lw== 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 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