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 26CC1CAC5B0 for ; Wed, 24 Sep 2025 10:07:33 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 8115B8E0017; Wed, 24 Sep 2025 06:07:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7E8DE8E0001; Wed, 24 Sep 2025 06:07:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6B0B18E0017; Wed, 24 Sep 2025 06:07:32 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 57D758E0001 for ; Wed, 24 Sep 2025 06:07:32 -0400 (EDT) Received: from smtpin25.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 253AA5B150 for ; Wed, 24 Sep 2025 10:07:32 +0000 (UTC) X-FDA: 83923716744.25.BEFAC51 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf23.hostedemail.com (Postfix) with ESMTP id B98F0140005 for ; Wed, 24 Sep 2025 10:07:29 +0000 (UTC) Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Re6o0pnj; spf=pass (imf23.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 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=1758708449; 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=8GrFljRltqv2IkALg1YfGWmZraH37YnKJBWkHZnJJ9Q=; b=2PAtp/kJxZsF0qunfjDH1iYhPIAGls8V4DBRLlJq3kswJ5+pMCNAarT2b3o3HdmL2hsbPC pc4jtwO9b3kokjsCxlMHMg5xhwYn20yG4yeeYcgVKo3BmXl7T9XQf8sUKBkWMusStiSMPe bxNeT77JifYFn9aKtiio/wQgWK8isnM= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Re6o0pnj; spf=pass (imf23.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1758708449; a=rsa-sha256; cv=none; b=wYHsZTHaY9J/oWbghWIQprmr9Zp2jCsYoeBwpSkmjb74oCUNNdrp/neZbtDe2+I6Ej1vk4 TEzxy1c7Q3nIohRhln9Jb1CHz2/fXb/OrXHu6yyeuWljbdad2khcZVppAA7ShvGoFHFhub CX6hlz1TTxvb7HI2+qUu7x6tCGB3Q7o= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1758708449; 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=8GrFljRltqv2IkALg1YfGWmZraH37YnKJBWkHZnJJ9Q=; b=Re6o0pnjZ+1G8+EITSCg3GFYNmG7YQI9s1OM9JaNj2a7wwny7N+TTZZfKP7tjGTjQ2zwSP hgdKQr5Aw1s2C3tdMDKX6KVmCI8VCBpqodxBYF3L0WeKqNnAD/0t9e/xzIHjUVzMKGGffy n+EXg1/GqbNYLJF6JJNIVwvWKIVbVlA= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-319-f1G8nltCNqS9n1MJ4HCoig-1; Wed, 24 Sep 2025 06:07:28 -0400 X-MC-Unique: f1G8nltCNqS9n1MJ4HCoig-1 X-Mimecast-MFC-AGG-ID: f1G8nltCNqS9n1MJ4HCoig_1758708446 Received: by mail-wm1-f70.google.com with SMTP id 5b1f17b1804b1-46b303f6c9cso28166085e9.2 for ; Wed, 24 Sep 2025 03:07:27 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1758708446; x=1759313246; 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=8GrFljRltqv2IkALg1YfGWmZraH37YnKJBWkHZnJJ9Q=; b=Rq81fNok/M8ujlOwdtmKQg07O8Y7BEcrgv4twizcXCqqAQ9WYpZLGfCt/JofbTvRI0 DY0B+HB6nvaYbGzelXOxp9jQfeCcyLhx2RLvYq3q8N5Zmusa0KazwZnvch56etfFYosR 2jlYJNyZ6YaiWi2z9YooNak/fj5hjIHRlCxW/coHQzTwM1Ag4rWzkt6v2V8aCJYGGfz0 4EdwPooOP0CcGbunPcLF2H/00isiUFwL8zoh4Cu8m/COYitk3Qe7D7jHOCNd8V5RyzU7 PsS4YQtobuITIHWYsPK9UNCOht4DBNMfL7HwJu1jDNKZuAVjlkmDGkMqscS3ECnYtWeM SuPg== X-Gm-Message-State: AOJu0YxYKbB/540LKXWJ1LTTZj5+AlrrPX7A3lzFKQNo1CjUJHhhJ6Ri GlKhEfnUbRkUgpd39RA++AaugIKTU9Cag+sEuaJW0uSrQafy27QU/4ywWQUcB86w8HUyg/wEQ9p Y9Me7/WHvlJ0Ki8FB0CsriRNF1yifqyXisOD89Wg0tRMQGtAoPufz X-Gm-Gg: ASbGncuXlF86BDOnCfRUDCjpKdZqSMf44NGxhvpGDkCP2ZnAFmacJ1LypI9gXFy4V5V C7TfrBPp87Ail12w+2PGSNEX3B8tke3M2/G5PZY/DvTTtJXelhpmugymJMeIShpiRQ/ftXyg0gz y2waeI1Jw5pbSXZSI0wg5IKFYeomaUT5N0EDYMeKzEmfYey5qO+eAuhcr742yrUOC5VXzC5Gkxr WS/SnxZYMg7Hj8w+94o0KXzL2Gqqt5BCTW1uKhlNmbCCx7iQHeG+H2sWv7m+FMFVCjPs4wYbsm0 9qDLo/HAftDdoB05oi4KppdPf1dR4n7zYLr61TSkvzE6KdBMxwMWnyTIuIIL7tWS/RKySzKTl93 Oks2EnlHwjvKGFgX3fUlQDoyq2Q6rzWH83yggA+5chg5Qu3MFEmLQmeTwKfy4neIRRA== X-Received: by 2002:a05:600c:c4a1:b0:45d:d56c:4ab5 with SMTP id 5b1f17b1804b1-46e1d97d834mr61858825e9.5.1758708445765; Wed, 24 Sep 2025 03:07:25 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFaQcC+ULZdp8/N6kG5WGhH1icSL2ZrXnUmEBTw0kMbgJba2jUfE9tmmYof9yvOb6DQDACnRw== X-Received: by 2002:a05:600c:c4a1:b0:45d:d56c:4ab5 with SMTP id 5b1f17b1804b1-46e1d97d834mr61858355e9.5.1758708445323; Wed, 24 Sep 2025 03:07:25 -0700 (PDT) Received: from ?IPV6:2003:d8:2f14:2400:afc:9797:137c:a25b? (p200300d82f1424000afc9797137ca25b.dip0.t-ipconnect.de. [2003:d8:2f14:2400:afc:9797:137c:a25b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3ee07411f4dsm27150172f8f.26.2025.09.24.03.07.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Sep 2025 03:07:24 -0700 (PDT) Message-ID: <0341cf34-9c20-4f25-9838-39871409b2a6@redhat.com> Date: Wed, 24 Sep 2025 12:07:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] mm/userfaultfd: don't lock anon_vma when performing UFFDIO_MOVE To: Lokesh Gidra , akpm@linux-foundation.org Cc: linux-mm@kvack.org, kaleshsingh@google.com, ngeoffray@google.com, jannh@google.com, Lorenzo Stoakes , Peter Xu , Suren Baghdasaryan , Barry Song References: <20250923071019.775806-1-lokeshgidra@google.com> <20250923071019.775806-3-lokeshgidra@google.com> 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: <20250923071019.775806-3-lokeshgidra@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: DfQ0qtxy0R2qp0Snwbjx5_u0YV7oeH8L30_gvybIN9E_1758708446 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: B98F0140005 X-Rspamd-Server: rspam05 X-Stat-Signature: 1iyq3kk4i871wnufdwo7qsdy7jykxhs1 X-Rspam-User: X-HE-Tag: 1758708449-285881 X-HE-Meta: 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 wWQ8m7uC 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 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 23.09.25 09:10, Lokesh Gidra wrote: > Now that rmap_walk() is guaranteed to be called with the folio lock > held, we can stop serializing on the src VMA anon_vma lock when moving > an exclusive folio from a src VMA to a dst VMA in UFFDIO_MOVE ioctl. > > When moving a folio, we modify folio->mapping through > folio_move_anon_rmap() and adjust folio->index accordingly. Doing that > while we could have concurrent RMAP walks would be dangerous. Therefore, > to avoid that, we had to acquire anon_vma of src VMA in write-mode. That > meant that when multiple threads called UFFDIO_MOVE concurrently on > distinct pages of the same src VMA, they would serialize on it, hurting > scalability. > > In addition to avoiding the scalability bottleneck, this patch also > simplifies the complicated lock dance that UFFDIO_MOVE has to go through > between RCU, folio-lock, ptl, and anon_vma. > > folio_move_anon_rmap() already enforces that the folio is locked. So > when we have the folio locked we can no longer race with concurrent > rmap_walk() as used by folio_referenced() and others who call it on > unlocked non-KSM anon folios, and therefore the anon_vma lock is no > longer required. > > Note that this handling is now the same as for other > folio_move_anon_rmap() users that also do not hold the anon_vma lock -- > namely COW reuse handling (do_wp_page()->wp_can_reuse_anon_folio(), > do_huge_pmd_wp_page(), and hugetlb_wp()). These users never required the > anon_vma lock as they are only moving the anon VMA closer to the anon_vma > leaf of the VMA, for example, from an anon_vma root to a leaf of that root. > rmap walks were always able to tolerate that scenario. > > CC: David Hildenbrand > CC: Lorenzo Stoakes > CC: Peter Xu > CC: Suren Baghdasaryan > CC: Barry Song > Signed-off-by: Lokesh Gidra > --- Acked-by: David Hildenbrand -- Cheers David / dhildenb