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 4D2B3C3DA4A for ; Fri, 2 Aug 2024 15:57:56 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DB3CD6B00A5; Fri, 2 Aug 2024 11:57:55 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D63A76B00A6; Fri, 2 Aug 2024 11:57:55 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BB63E6B00A7; Fri, 2 Aug 2024 11:57:55 -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 9E1396B00A5 for ; Fri, 2 Aug 2024 11:57:55 -0400 (EDT) Received: from smtpin13.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 5BD001C4B75 for ; Fri, 2 Aug 2024 15:57:55 +0000 (UTC) X-FDA: 82407761310.13.EF83C19 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf15.hostedemail.com (Postfix) with ESMTP id 05560A0011 for ; Fri, 2 Aug 2024 15:57:52 +0000 (UTC) Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Sj9MWFFx; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf15.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1722614208; 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=o8CyxVqweIF0ieon88U7x8sp9PNeNO828g6IWuk2Csg=; b=re/i4HRTmBs94omo2Oeds/bwYBJkCHeYHkPazgWXDkNORprQxw4nFR14NKWQUSdLn1ZYRV VXASvHjJ45RfDIknbvfYNNYKnG0pEz7lBM2fAGKjxfT2pMzE6AdBFBU0jbSpvUu42rlbNp VJmHIQXY/MrswH0MFWhBevxA7vvq3RE= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1722614208; a=rsa-sha256; cv=none; b=pPRWNvBpzP9CUKr9TR6/iYbQP3E7PvIRmfOeWTrYstjezqP14WCHRdKa+N3VJTZnWb9km2 87i6xi0oOCyD1W4XUFm9tI+YcVvUfxCpY+IU64ncHJmjenjXK0JJKqyjafdxc4FkiBZw2D C1wnXTyMYscUkJF6q0vtmOtYlqGdjas= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Sj9MWFFx; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf15.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1722614272; 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=o8CyxVqweIF0ieon88U7x8sp9PNeNO828g6IWuk2Csg=; b=Sj9MWFFxUgI/K7g5/7GTPVynLlZZiNJ1fJuMVG7bJvrsideshMW6pSnxN8SklSR6cOViIF Ebn7n7FPOAqZFmBloPbXgCT4xKxQ3avJyHr10YhcqAQedJtGj//Dv2e+ipwl+eZNqurD5U QSxI8XCJOADNGzQgCshsl2Hw6PNOPuM= 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-352-IsdaLAuTMH-g-1MhFXSfhw-1; Fri, 02 Aug 2024 11:57:50 -0400 X-MC-Unique: IsdaLAuTMH-g-1MhFXSfhw-1 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-428c2fbf95eso17727225e9.1 for ; Fri, 02 Aug 2024 08:57:50 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1722614270; x=1723219070; 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=o8CyxVqweIF0ieon88U7x8sp9PNeNO828g6IWuk2Csg=; b=M4fGOAkBtX1yrFMfOl7K2sC9BU/TqnCs3liYl9NTauo8COzOWrp2FTzL6peFR5g4fQ 9Mbb/Lv3LstlJa7bZQHPtlaKPaGYSznFpcYo7Xz4DPiYXgFuQl5mrB/FGIIU5hmmF7AV HCRCSyCGTnkddSeB5OAaVA1THJHKAtq3aXE+GAW4ny1wEjEalCdvcYYMYCHEMJ10Cjvf t8nLgZC59fKaLx75Zj6sdkbcaWcNbgAgY4a+JTqVxfImlI8fFdFy6yChrvqJQW1HdTyd INQ8dcwiVHIf1Lhk7pbGSs2y3jBpdSh0yIei/htMoHtW0us9qg6bawWnKtmYhcOEvTlz reSQ== X-Forwarded-Encrypted: i=1; AJvYcCVEuP+jLbGbSAhEW54IhLIm5LqjWE2+naBoqXb2soLUYNlyAKipiRCoxis3g0tqcC1UbDS64u1gvNKGsjJiUt9hPZ4= X-Gm-Message-State: AOJu0YxKCPQgzsNAI/hN6vDFkToqixrhnEZvUwwivXhg5q1xnm9cl38T D8KHejUT9F1KBl7muwP6/NrIHqVjRWNbFz1sd67jMIAfSmKkTgTnKt77Kw59Qr9RMJ5wYjmdmGd 1yhXUJ5Tm8Sw7olwqfKn4MKuOj1fR2XJa0+Vi8MtUy9+KWSK7 X-Received: by 2002:a05:600c:3b92:b0:426:6388:d59f with SMTP id 5b1f17b1804b1-428e6f88ab5mr25998125e9.1.1722614269689; Fri, 02 Aug 2024 08:57:49 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEAB/iWp0kcpjrY5OhvPv/Oyo/lMW/wjh0JrgfYiA+llWqgY/XCkve1AK7hUM/XO2A+l7mNIQ== X-Received: by 2002:a05:600c:3b92:b0:426:6388:d59f with SMTP id 5b1f17b1804b1-428e6f88ab5mr25997875e9.1.1722614269088; Fri, 02 Aug 2024 08:57:49 -0700 (PDT) Received: from ?IPV6:2003:cb:c717:e700:a3df:9aa8:9edb:dcac? (p200300cbc717e700a3df9aa89edbdcac.dip0.t-ipconnect.de. [2003:cb:c717:e700:a3df:9aa8:9edb:dcac]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4282b89a86dsm98639065e9.1.2024.08.02.08.57.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 02 Aug 2024 08:57:48 -0700 (PDT) Message-ID: <1ea7a0d2-e640-4549-ac0e-8ae0df8d8e6a@redhat.com> Date: Fri, 2 Aug 2024 17:57:46 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 05/11] mm: Add fast_only bool to test_young and clear_young MMU notifiers To: James Houghton Cc: Andrew Morton , Paolo Bonzini , Ankit Agrawal , Axel Rasmussen , Catalin Marinas , David Matlack , David Rientjes , James Morse , Jason Gunthorpe , Jonathan Corbet , Marc Zyngier , Oliver Upton , Raghavendra Rao Ananta , Ryan Roberts , Sean Christopherson , Shaoqin Huang , Suzuki K Poulose , Wei Xu , Will Deacon , Yu Zhao , Zenghui Yu , kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20240724011037.3671523-1-jthoughton@google.com> <20240724011037.3671523-6-jthoughton@google.com> <37ae59f2-777a-4a58-ae58-4a20066364dd@redhat.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: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 05560A0011 X-Stat-Signature: g3qsz8jh719o5am4hgsukn98nayy3th7 X-Rspam-User: X-HE-Tag: 1722614272-603945 X-HE-Meta: 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 ooAdqRNx sN42oG51t7JdoHiqXkgQl9tjwsXoEVAtQTJQWEWOH7vx3tVdQBJ0vi+hFzCO6+YQj5ToEtJW6zKLwSnIECC3tCOl5Suw79hFOVutcrD4CrJ5U+DDnGChjMvaMsjRxd0qQBdetmKnmd36JHwl/eJ41e6UcrQcbj3uUJF+IOWGqzuIIdGODVuCasdraFCYBKEkjsQEv8w2J7063j4S8YBKEFGwcwQac6FHzcexTKTV9HwPMhJMnmVwcrBMebrqE+eh3BuHVIRQohLFBanzxLLXzJFNHc3o6rMmFPl2NyeENWFzDadP73TwnMmO1sWMheGNdFMJ9pRd0nLYxyw4BwDciXlFnd3Tr2qYnnhoJ6Tj2exhoweeoctfTm7V9Ou/mhzYvqNUFE1katMIdVIochMPHETKV2m9IOjmelUWcsDBN0W1UrXk= 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 02.08.24 01:13, James Houghton wrote: > On Thu, Aug 1, 2024 at 2:36 AM David Hildenbrand wrote: >> >> On 24.07.24 03:10, James Houghton wrote: >>> For implementers, the fast_only bool indicates that the age information >>> needs to be harvested such that we do not slow down other MMU operations, >>> and ideally that we are not ourselves slowed down by other MMU >>> operations. Usually this means that the implementation should be >>> lockless. >> >> But what are the semantics if "fast_only" cannot be achieved by the >> implementer? >> >> Can we add some documentation to the new functions that explain what >> this mysterious "fast_only" is and what the expected semantics are? >> Please? :) > > Thanks for pointing out the missing documentation. How's this? > > diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h > index 45c5995ebd84..c21992036dd3 100644 > --- a/include/linux/mmu_notifier.h > +++ b/include/linux/mmu_notifier.h > @@ -106,6 +106,18 @@ struct mmu_notifier_ops { > * clear_young is a lightweight version of clear_flush_young. Like the > * latter, it is supposed to test-and-clear the young/accessed bitflag > * in the secondary pte, but it may omit flushing the secondary tlb. > + * Probably makes sense to highlight the parameters like @fast_only > + * The fast_only parameter indicates that this call should not block, > + * and this function should not cause other MMU notifier calls to > + * block. Usually this means that the implementation should be > + * lockless. > + * > + * When called with fast_only, this notifier will be a no-op unless > + * has_fast_aging is set on the struct mmu_notifier. "... and will return 0 (NOT young)." ? > + * > + * When fast_only is true, if the implementer cannot determine that a > + * range is young without blocking, it should return 0 (i.e., > + * that the range is NOT young). > */ > int (*clear_young)(struct mmu_notifier *subscription, > struct mm_struct *mm, > @@ -118,6 +130,8 @@ struct mmu_notifier_ops { > * the secondary pte. This is used to know if the page is > * frequently used without actually clearing the flag or tearing > * down the secondary mapping on the page. > + * > + * The fast_only parameter has the same meaning as with clear_young. > */ > int (*test_young)(struct mmu_notifier *subscription, > struct mm_struct *mm, > > I've also moved the commit that follows this one (the one that adds > has_fast_aging) to be before this one so that the comment makes sense. Makes sense, thanks! -- Cheers, David / dhildenb