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 7D835CAC5BD for ; Mon, 29 Sep 2025 07:25:43 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BA6B48E0003; Mon, 29 Sep 2025 03:25:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B56138E0002; Mon, 29 Sep 2025 03:25:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A1E638E0003; Mon, 29 Sep 2025 03:25:42 -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 89D2E8E0002 for ; Mon, 29 Sep 2025 03:25:42 -0400 (EDT) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 36CC98603E for ; Mon, 29 Sep 2025 07:25:42 +0000 (UTC) X-FDA: 83941452924.14.91D278E Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf14.hostedemail.com (Postfix) with ESMTP id E7C5810000E for ; Mon, 29 Sep 2025 07:25:39 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=UdJNwF0s; spf=pass (imf14.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@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=1759130740; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=4sy/3KO2tjGWTLYogygfceE41CTUap6pmBFJxNyOknw=; b=rOHZZ7v5bzMkzT5dMBIhLWgxcYVhCVnfI1PaLNH9BiKoAargAu9BeqL7SBQfX+3z15yiwx AQFEg1kvY+vNx2jEb4QaG8y4PFubp1PP9eVW0ILfAl4KEt0+hJbG22IrCGYxqWk3WCSARC z2qLARWS3N5YkdGumlObe6eEdmLrN1s= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1759130740; a=rsa-sha256; cv=none; b=ZxPm7T/iLTSiBqXpJ9TZ7l5oBbluQ8Km1z+0+zEsc7KyXt5jgHzkZlrhrlzGh/MM1I+AZF HSuRTWnI90Dul4xzs4p9sTimCvJv7nVn6jsYNJ93efJW92GeWmNPQ22HdW4ejqVAp3/Mqo mqSmvxzzmWjL4Hbed/IBNNxhAGl8go4= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=UdJNwF0s; spf=pass (imf14.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1759130739; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=4sy/3KO2tjGWTLYogygfceE41CTUap6pmBFJxNyOknw=; b=UdJNwF0sdJbVcODt7JDX3CIgWhQM4rF1n7uE62qFr/De4TGnx8xcfr3iLuHpU/e4YJ9nuy DLD5dK3TDeEvztWWw4zVWHcLpxkrQub20+G2m5qLpQGckjOJ9J6sYmCFv2UFeXaryZRHjd sE6J7vLPjXZ63aAuSA/usGLV/yAZ7A0= 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-688-jWo6zMivNiW9UWwdvc7q-Q-1; Mon, 29 Sep 2025 03:25:37 -0400 X-MC-Unique: jWo6zMivNiW9UWwdvc7q-Q-1 X-Mimecast-MFC-AGG-ID: jWo6zMivNiW9UWwdvc7q-Q_1759130736 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-46e31191379so27408605e9.3 for ; Mon, 29 Sep 2025 00:25:37 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1759130736; x=1759735536; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=4sy/3KO2tjGWTLYogygfceE41CTUap6pmBFJxNyOknw=; b=crbT1padti1h50uqB1xl9t7P7AzswKW53KECxuTfrR3JUC2llT+twpVckVVsir4HTR lqLQ10vgGpRmDpA2dlye8PJ2N0EZuWi7n+q+p/mQiCyP8sf6oTmsc3evDsQP0W9o7QPc d9TqD+rV4INHRvWpWVH2tYBsqsrhzPIr4s/sACVLbmYt7igkHxjbuZpnyoIGzc1bHDB1 9UZEIp542DN35el4TVs7pUfZabSBHXkjY7TTNAS+8Brvjqyvm8wPiySMNb+JVegJxFC7 JP/IuI4Y+AhBsg55fCAYcC/zYLzepn+pdQQnCJWyUxlz5BLmE+4pWp5yTVcM5I/ospst R6OA== X-Forwarded-Encrypted: i=1; AJvYcCWP9AX3nMvpOw+VxkYoBBQrC+3+0OqrdB6NMnarPcGebpM9lxM3GYFGzT+xery079a4+qnODNz6SQ==@kvack.org X-Gm-Message-State: AOJu0YxCIsNZB15M1gjEpjJsGOMmI8+NOQo+qnf5Wrwai0AyWzYvtpdF Wrqc38AqOAW5IdNldYfmUGUNTAGSD/qbKlmFbhbJKZfd2YlGemmGFlzWSa3ym95JzPt5CNJgHjd 6F9vFpoUN5qlpBj/TpLkZ4e5DLoj02Cjbyb2BxIybr+VukryMR6hN X-Gm-Gg: ASbGnctOilCtEVKbvwMvyqmd25YyPfXqMcx1WZsf7bwXsKfPvWC2FNAddMpJdN0ByHI 2o6AzEDy2kmb4CFnpSdSmzrxKkx8HtwLtdaWZWgvQ7HtC1DGShLnq3ckQV+nOnC+QJOv0oMDS4J x+3CEp3j4XiJTxG1ETU7anJkQaSbIfi6tz88nAfN56hgXDHnmTuM97d9nbdmg4oT+cIWg+xCcJ7 c98ZYsQgsByg4p+LMrV0atLoeuRSReEVy9eVeyfYRgNG0XSBxpJmKYtgZmHwM/f9wfG7o2Gu3i4 rhpO+BvrAf7me6eRviCFTR/A9WjhIA/rxZ/5wCh1ON73H5nhSOMkKazBTO3zZ0Up/dJKeV5LzaH CTwAuqFCGMx/S8hkMOi/rwZTwxZynOhnSfDhTEPANwdYjHbGtuIhL2tQYVCXs/WofbQ== X-Received: by 2002:a05:600c:c0d5:b0:46e:4cd3:7d6e with SMTP id 5b1f17b1804b1-46e4cd37ec1mr23407135e9.9.1759130736295; Mon, 29 Sep 2025 00:25:36 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEC8JA6ojG0RK/BWOWXqdIdPR54HSGF6zZtmicAMPJN4Os7iy+ZeWmHixT2nGgDQSTRkKabRw== X-Received: by 2002:a05:600c:c0d5:b0:46e:4cd3:7d6e with SMTP id 5b1f17b1804b1-46e4cd37ec1mr23406905e9.9.1759130735908; Mon, 29 Sep 2025 00:25:35 -0700 (PDT) Received: from ?IPV6:2003:d8:2f05:e100:526f:9b8:bd2a:2997? (p200300d82f05e100526f09b8bd2a2997.dip0.t-ipconnect.de. [2003:d8:2f05:e100:526f:9b8:bd2a:2997]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e2ab31f1dsm212404725e9.13.2025.09.29.00.25.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 29 Sep 2025 00:25:35 -0700 (PDT) Message-ID: Date: Mon, 29 Sep 2025 09:25:33 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/rmap: fix soft-dirty bit loss when remapping zero-filled mTHP subpage to shared zeropage To: Lance Yang , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, baohua@kernel.org, ryan.roberts@arm.com, dev.jain@arm.com, npache@redhat.com, riel@surriel.com, Liam.Howlett@oracle.com, vbabka@suse.cz, harry.yoo@oracle.com, jannh@google.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, usamaarif642@gmail.com, yuzhao@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ioworker0@gmail.com, stable@vger.kernel.org References: <20250928044855.76359-1-lance.yang@linux.dev> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20250928044855.76359-1-lance.yang@linux.dev> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: EP7NOyAIgJ2LNyDSvFtCgaN17ob1kYxNYQDG6ALt9-0_1759130736 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: E7C5810000E X-Stat-Signature: jc4wjwikk1ymeojsz5fd5j57cgszdfof X-Rspam-User: X-HE-Tag: 1759130739-442092 X-HE-Meta: U2FsdGVkX19KQ2XZukwGyX6xFAPRCkr0Y9SODn7BRkAPm36Ur8hhoh4n9InJhndcAxFteRQ5UjHOTVfRQQsnJJ5NIrMld5rDvYdMpU/UKGl7gFKhwSvNuzU8eoJsegUhmoHuHdJddCHpJhIKtvJA5abZsGoigdnkEEOT6y7D8j4qqodMlRPX/kw2m1oKkN6kDdcIt2xkoPg5sZ2ngeZfNgQKaMo5GctD9LvWkb1CAZJ/sJMk5nIsCf+GxOm6sq+Kq1i7ptU13aTST+YN7ahET+lPQoI4kt6vX/PgzairapyUx0nUXgNuWkyAhLIjwJ9cKWsYK0kNK3TrThe0oclfsXTIoxx97/6+xP7lHQQUnD8Tr6Tz5Mfa9kDZMjCYWa/n6vYeGUobemMWkbCURLNSqal5VhLyxmBy5JyL+QKDwwY3Yv1pG9fitE8O96IFFD3tcMYLI7j8guQO4c9vMdtd0NoUjojp8/yPUCkMrDe82JWigZXlvHQB8bul8xWL/LxwynrImRoRv0qfUbIYSoTbMgK8z+D8+qXX71YM4EEhOoKAfEeFPDBXMAWTdRRQWsqJtzQBxhbhn76Jcxw+fL8VePPTERTqztPVeQudIieJaZpLSTP+mA5gnu6ZYRYlqyd2DI0yDiz9utgkMO4EehK2zG53G91tTk2P8C6qjh/duQ6j6aku+fCpReRYUgzhwfvSJzQaPHJlGy7akqPzLcjdZnaAnKUUoUqvuBqRnu62UQQmC2Qsvnm6YSD/02Z1nOEa7wGeCC46rj6+4P6Bss51dGyhjYJXcarBHm6UzROgaGXfvnlTwRCOKLhqqT396jlVsxLoK/VxnmPtsx8NzcNgg7CnFhEVmseIKlpGz/+pr7fAtEcrVYz5u0zjNtxhUMGnxng7l3BSC8FnPE5y08EGnyiZnmad6WsYm8zAOxCyVytYiHgp0TGwag3kkJf3GOaKBbKrbtrSh+mdZXnbU1j fYxAlHdG tXj3Rv4/p1z6nISqIHIs30o6z1YBjf1s9G0QML+DIAyU59UWHPmMP9c5rgFoVJBwbdBHIYk7tWqyag5HUG3rd45x7lRzClZAh4WuwzY/Sykau0G4= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 28.09.25 06:48, Lance Yang wrote: > From: Lance Yang > > When splitting an mTHP and replacing a zero-filled subpage with the shared > zeropage, try_to_map_unused_to_zeropage() currently drops the soft-dirty > bit. > > For userspace tools like CRIU, which rely on the soft-dirty mechanism for > incremental snapshots, losing this bit means modified pages are missed, > leading to inconsistent memory state after restore. > > Preserve the soft-dirty bit from the old PTE when creating the zeropage > mapping to ensure modified pages are correctly tracked. > > Cc: > Fixes: b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp") > Signed-off-by: Lance Yang > --- > mm/migrate.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/mm/migrate.c b/mm/migrate.c > index ce83c2c3c287..bf364ba07a3f 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -322,6 +322,10 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw, > > newpte = pte_mkspecial(pfn_pte(my_zero_pfn(pvmw->address), > pvmw->vma->vm_page_prot)); > + > + if (pte_swp_soft_dirty(ptep_get(pvmw->pte))) > + newpte = pte_mksoft_dirty(newpte); > + > set_pte_at(pvmw->vma->vm_mm, pvmw->address, pvmw->pte, newpte); > > dec_mm_counter(pvmw->vma->vm_mm, mm_counter(folio)); It's interesting that there isn't a single occurrence of the stof-dirty flag in khugepaged code. I guess it all works because we do the _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma); and the pmd_mkdirty() will imply marking it soft-dirty. Now to the problem at hand: I don't think this is particularly problematic in the common case: if the page is zero, it likely was never written to (that's what the unerused shrinker is targeted at), so the soft-dirty setting on the PMD is actually just an over-indication for this page. For example, when we just install the shared zeropage directly in do_anonymous_page(), we obviously also don't set it dirty/soft-dirty. Now, one could argue that if the content was changed from non-zero to zero, it ould actually be soft-dirty. Long-story short: I don't think this matters much in practice, but it's an easy fix. As said by dev, please avoid double ptep_get() if possible. Acked-by: David Hildenbrand @Lance, can you double-check that the uffd-wp bit is handled correctly? I strongly assume we lose that as well here. -- Cheers David / dhildenb