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]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3BD4ED75E28 for ; Fri, 22 Nov 2024 11:10:41 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C51448D0008; Fri, 22 Nov 2024 06:10:40 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id C01788D0007; Fri, 22 Nov 2024 06:10:40 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A52C48D0008; Fri, 22 Nov 2024 06:10:40 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 865F28D0007 for ; Fri, 22 Nov 2024 06:10:40 -0500 (EST) Received: from smtpin13.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 2AACC1616F3 for ; Fri, 22 Nov 2024 11:10:40 +0000 (UTC) X-FDA: 82813460268.13.43AB721 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf27.hostedemail.com (Postfix) with ESMTP id 0DF454000E for ; Fri, 22 Nov 2024 11:09:38 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="de/I7QkQ"; spf=pass (imf27.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1732273775; 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=WjuvFzSNk1HRpi+DS7yr7jLFl3FSsGwM1+OucgYZlwA=; b=se8F+S5v71j1D+KuWS29p9Sv/zt2NYdFlFU3rGX/6/4DAfrNAVikJPLGPcF1b4IDarcaFv AlkW2olZUGjRqopUnxeH8DLsHNMMcDfoKF6zhA6eOyqkxJ4THGzvugyq0pezMg1kAIJ2XS MkR8e6c0KeSZd9ee93vXoRrKH+xijKM= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1732273775; a=rsa-sha256; cv=none; b=BuYb62UsQzSpw4z5oofkUiphBNFUgj2Fs5eT/uyZozfnxlWSyUfPUIERSAORjz5r4CDfL4 lJ4S5CdlQubnOXnY3bsmakONMMPI6FE/9QH2UGl3pjeROmLfjL8zZgus5qgqNhUcqWQHAF AnoWLEmjsha+8ZqO2waMx89K+QeJN88= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="de/I7QkQ"; spf=pass (imf27.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1732273837; 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=WjuvFzSNk1HRpi+DS7yr7jLFl3FSsGwM1+OucgYZlwA=; b=de/I7QkQG2m5XWiJnAp5vSOXGo47xok1oAWmOrXjvebBrT1HUD1zx8jZUgAk8uZOVatPWI +Gd4+s95U98bx1sJ5g7KhTmmqX30crxogc49H4ORYtUFEeA2HfnfWW6VWKbIlM18Sz/GNY jlDHx5IJJYqJRL7KYJZEms00batRd74= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-644-9PNWi7EtPhiWoZg5l6ZJbA-1; Fri, 22 Nov 2024 06:10:33 -0500 X-MC-Unique: 9PNWi7EtPhiWoZg5l6ZJbA-1 X-Mimecast-MFC-AGG-ID: 9PNWi7EtPhiWoZg5l6ZJbA Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-432d9bb0f19so15962865e9.1 for ; Fri, 22 Nov 2024 03:10:33 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1732273833; x=1732878633; h=content-transfer-encoding:in-reply-to:organization: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=WjuvFzSNk1HRpi+DS7yr7jLFl3FSsGwM1+OucgYZlwA=; b=brZppd/6XL7edGEQiUsXkW8oEQ7BfSqonf2MjqNF3viz3O5FLOT8PxgYCKQFrjuLV9 yJ/IDvctZVQP8hhrcWs4MU/VY/zRMOvvpsrrhut3A5Yr5KjTJkqZs/7kkgZDqyNYzV+9 nV55R88mf8M/mYO2TF3mOqazBWPjZc+6XroAhsvnTyDyDUqfmcNxRNID/eCebx0agxk9 2VzBQdaUnxgplf/TJah4DYX04ekDTc80WRh3DkfZY9Ko+DYI8FkNvQlNq0L/jjJ+wE11 8wErMGLdYVMJtAjeqlusbUy+0F7cwzO1JFa7yE1EWZRTDNUOnEiHR0iAmnp3qDH4VCWL w8eQ== X-Forwarded-Encrypted: i=1; AJvYcCV3bruzDdrktp+ZF/E1wKf+689lLTiKwHwutaLQ1qlt6hFiWLfttUrzRdK9z1GbW977FZsKbi440g==@kvack.org X-Gm-Message-State: AOJu0YyoyiNAkWHfkJWg0a4RhER6jHTqM1z5+bEkq26nc0wHA/D6pdxJ 5Dk2Tc+lIXG4sLvW1qpHCWQ6dEudGW1P5C/s0bQA6DHFeZcOuwWdxM/QOqZXSBrDVGl23chSd1G cesSCi7w3T0GM0BqalaCzxqIqCLE3KbQxoVQtl8yFLiBaSmZd X-Gm-Gg: ASbGncvuUOUCRHTztmjYSjXplg7QIXveQlxvH/hFTiGGMfdzesQcyqH/MzFjQhYkbu4 QEGn9EwBeWwUG368nn1rwAMNjHwM+FBPLwecx64ACS7nBLRiupTWyNYDeps+V4zRpoxdH9Qnc4c T4dJ+VVJeOexWqOU5qXWCBu8rw/Rt2yKTc7nBwNfmgN67SJNwmkdIpHyvAEzcORcPk9HGfy64s7 JgtQZfm7hoOU4jbpbaWkJPwe5TVUSx2qxBnjCDi6oXfCBXUgF52Imld/m1DVT/x/hpcfaQoLBTa zcVHKYwveIIsTY5+GpQpE/me9bkeuWO9VwtYsrq23BHJZHGy3MyOZIwmX3EZZwp/cl8CHNqEBg8 = X-Received: by 2002:a05:600c:917:b0:428:b4a:7001 with SMTP id 5b1f17b1804b1-433c5ce57d3mr59075935e9.15.1732273832724; Fri, 22 Nov 2024 03:10:32 -0800 (PST) X-Google-Smtp-Source: AGHT+IEeYMDb7+3fkk7/17y2EpOUO4usDkj+WgYyjOGc/JOqT/cbixRvnDnT5jJtPNoIoj7vn6Vy2g== X-Received: by 2002:a05:600c:917:b0:428:b4a:7001 with SMTP id 5b1f17b1804b1-433c5ce57d3mr59075515e9.15.1732273832391; Fri, 22 Nov 2024 03:10:32 -0800 (PST) Received: from ?IPV6:2003:cb:c70b:7a00:9ccd:493:d8e2:9ac8? (p200300cbc70b7a009ccd0493d8e29ac8.dip0.t-ipconnect.de. [2003:cb:c70b:7a00:9ccd:493:d8e2:9ac8]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-433cde8c6casm23630315e9.33.2024.11.22.03.10.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 22 Nov 2024 03:10:31 -0800 (PST) Message-ID: <46aa36f0-64a6-4aee-8134-0ec93f62e59c@redhat.com> Date: Fri, 22 Nov 2024 12:10:29 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/3] seqlock: add raw_seqcount_try_begin To: Suren Baghdasaryan , akpm@linux-foundation.org Cc: peterz@infradead.org, andrii@kernel.org, jannh@google.com, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, vbabka@suse.cz, mhocko@kernel.org, shakeel.butt@linux.dev, hannes@cmpxchg.org, willy@infradead.org, brauner@kernel.org, oleg@redhat.com, arnd@arndb.de, richard.weiyang@gmail.com, zhangpeng.00@bytedance.com, linmiaohe@huawei.com, viro@zeniv.linux.org.uk, hca@linux.ibm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20241121162826.987947-1-surenb@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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20241121162826.987947-1-surenb@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: DVCqEQGYwn606X4CFsvgpCnSImS4-mqooAWSaIdYFss_1732273833 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: c5f895hkwj6fpsbfsxr1b81ymhdrbzj1 X-Rspam-User: X-Rspamd-Queue-Id: 0DF454000E X-Rspamd-Server: rspam02 X-HE-Tag: 1732273778-471322 X-HE-Meta: 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 Sk+Dk/vH vfELrzXK6P9u+2IobM6pAs/j0YPEmfzYijCM4M85XQdDniiY6bfQ2UifqMoG4KDFAR/O78+ioNRlEMg3z3eCLI7dy27Qs+xKgIIKH1GR2jDyHwPQZbOaKHWr64U0UcgfzbQlVoYwTAPBW4zxvoq+73Mp/m6ASdh0Ohxx2FgCwfXox98wtwA7mo0AFJf1NFTBNrVv/IOBryinTBAlrZ+PVJIaL0SBYocaG+XsaNbjFUkXPMc/ugr7FJb+xqFW/Y6JAAC/IeECbLD13Lr/TPfD99qZ3BaDC8xiWl5/1473BeMZiPC63f/9Fds+1x7ZaLrQhRcmiG6NPoCPdnQ00qNOKeVicK2K2fbHT0eRKeHQm5u0ENztkAFUS7oY4sI2dSStWEF4wIu3O64qKSJg2tEF0rf9oFOgNWU+B8FtuSIg+8XH/AOoEdL5oH97cw2ZBcQmTElw9ZaHAdMQKt0/foYo89PzlarfyDJEXItAHIzWT+lMrV6VY0Eof76OFYGtPiucBFIHnvpEDpUdg+kTVQTYp+vbaJ+OmkRrsOlq8y8t1L72iJGqZewNHS89TG2vgJj5r96IuIapsXZN4jd33P/Vk8+5SMvE5XF/1r+1D 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 21.11.24 17:28, Suren Baghdasaryan wrote: > Add raw_seqcount_try_begin() to opens a read critical section of the given > seqcount_t if the counter is even. This enables eliding the critical > section entirely if the counter is odd, instead of doing the speculation > knowing it will fail. > > Suggested-by: Peter Zijlstra > Signed-off-by: Suren Baghdasaryan > --- > Applies over Linus' ToT > > include/linux/seqlock.h | 22 ++++++++++++++++++++++ > 1 file changed, 22 insertions(+) > > diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h > index 5298765d6ca4..22c2c48b4265 100644 > --- a/include/linux/seqlock.h > +++ b/include/linux/seqlock.h > @@ -318,6 +318,28 @@ SEQCOUNT_LOCKNAME(mutex, struct mutex, true, mutex) > __seq; \ > }) > > +/** > + * raw_seqcount_try_begin() - begin a seqcount_t read critical section > + * w/o lockdep and w/o counter stabilization > + * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants > + * > + * Similar to raw_seqcount_begin(), except it enables eliding the critical > + * section entirely if odd, instead of doing the speculation knowing it will > + * fail. > + * > + * Useful when counter stabilization is more or less equivalent to taking > + * the lock and there is a slowpath that does that. > + * > + * If true, start will be set to the (even) sequence count read. > + * > + * Return: true when a read critical section is started. > + */ > +#define raw_seqcount_try_begin(s, start) \ > +({ \ > + start = raw_read_seqcount(s); \ > + !(start & 1); \ > +}) In gup_fast(), we simply do seq = raw_read_seqcount(¤t->mm->write_protect_seq); if (seq & 1) return 0; Should we be using that there as well? if (!raw_seqcount_try_begin(¤t->mm->write_protect_seqs, seq)) return 0; -- Cheers, David / dhildenb