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 08B37C28B23 for ; Thu, 6 Mar 2025 09:19:52 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0CE55280003; Thu, 6 Mar 2025 04:19:50 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 02E3E280001; Thu, 6 Mar 2025 04:19:49 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D9B46280003; Thu, 6 Mar 2025 04:19:49 -0500 (EST) 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 BB9AB280001 for ; Thu, 6 Mar 2025 04:19:49 -0500 (EST) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id D60041412BE for ; Thu, 6 Mar 2025 09:19:51 +0000 (UTC) X-FDA: 83190578982.12.44CEE94 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf03.hostedemail.com (Postfix) with ESMTP id 3EA2220004 for ; Thu, 6 Mar 2025 09:19:49 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="QBhL/fJ1"; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf03.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1741252789; a=rsa-sha256; cv=none; b=fLd3bP/OaRzvNjI3RHve+F+bhriPLXAudI76wxNJtCABOpVxcljPZl5SqVt+cLMWRpMZRj c1IeNuk25T/MN+6GWI1n/78P8DT+Msa5kKtCLoH4SzZRyl7xoR0r9wPhFOznLpanF7lyzw dVfieWsqDZ3nu3e7V1AhZ9ih1PkS49s= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="QBhL/fJ1"; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf03.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 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=1741252789; 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=j4u9DLEhIx3HFuqYUpbNqKrefyTEPoTUC28xU5Dyl5E=; b=PkOThu3TXdW5rSJd+xTCztmTUMut7UzveWY4HRsd7besQU0qFe34GpL9RNxFqPLfWfwOGY +rDEJRYmg545SL4v4C7/0Nq/WNO+NuLdrA4WO1Hs/bJAyCtoNc0R+WFFzy1uor7XUkUbMx SSgTUQtCVbeNM050SZcvdQzpLtbqgyM= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1741252788; 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=j4u9DLEhIx3HFuqYUpbNqKrefyTEPoTUC28xU5Dyl5E=; b=QBhL/fJ13eWOszQv/fgRjMvnfkpVc5pjo27tZ4jxMsFyBl5E9DD1IkSoQulh1DqbdrzUrG lZJCjE9j8D0AueKGRHJJiA/g1YzZWbkxzfJqRD7+Qb4MNPE21iMl4v3YiYE7txxmGPWcr3 spseNNKFGObFu5D3DGBfd1iWXMx9lEQ= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-301-v483oElrOMGdCcnob26vyA-1; Thu, 06 Mar 2025 04:19:47 -0500 X-MC-Unique: v483oElrOMGdCcnob26vyA-1 X-Mimecast-MFC-AGG-ID: v483oElrOMGdCcnob26vyA_1741252786 Received: by mail-wr1-f72.google.com with SMTP id ffacd0b85a97d-3910fcca0c7so173069f8f.0 for ; Thu, 06 Mar 2025 01:19:47 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1741252786; x=1741857586; 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=j4u9DLEhIx3HFuqYUpbNqKrefyTEPoTUC28xU5Dyl5E=; b=xO6y53M28O7KciF0KaAF7yJHWuCA9OLkVzfxtLM2e1s3x7PhIm3N75/YQvehiApvBb LifU/MJmF5HifXA0j6g5usT5uQnPcs6r/NcmRmOL5z9OA4cRcP742z+Q7eqiIUW5gNoq SePiymtg27asdJzrzgKcwoeAN5DWsqQppflNTTUKw5WaUIyyyt/r3xo4zrccaFWEcvxp ABj73rfbVclkMuFTCFfPzuIIBanEzo9gO4FJuNcIQsw4wiVegh4ogfTf18EmWlLZVvSJ IvnfV8YCRf8urbf2BPhkr+ToofZ3NAX7EOVgkWpX0/Va8f96OnJg/DJSc2fUE9AtPVb0 Oq6w== X-Gm-Message-State: AOJu0YwJzDe5gKYk4CU5d9oOR5IKEMq/w5tvxLKCS/NSpsQYz0sWSx8R nIlQY6DY8GCDpUzVX8ug/DS6Ts+7PsTRBDvaSaA0ydpLg1IbNnpimt7cxxfK/uFkZ4gjTrbjyPg 0ub8O7F8qqOg+/XvPXqNTjqgE9qAo3SepsbuftMlud9axT9Nm X-Gm-Gg: ASbGncuEWjdzkt27lp3P+vjEVOj1qkjiWLMQYdQCL1Jro6tlZvIXd8DbgsYTuMwZJs1 wjhveRg36wkLEIPhYidnpMzTDCogZneLxAFNLNiGOgh9zupzoks6icuplyTGyQd5u941gvzfmVQ azpzl6i5OF9j52HPr/6KvLWIejF0sI85723CPZ4tz4uUHTwpd9UIXdvCjBuLajUmG+FlLGjZOy2 mATiFBCvCmTKvUlnyFM9Z7TFmCaLAR5k7kZ0czu70W2pSYXN9r7CWx82850mC0KODVTLPNqZJ7b AedrLXK27P8PyTQIUtIIw24jC/qyDuq4SqvnvVweGoMdAvcLTiCha6zluQKyVXYoMLxYbg/7x06 DQ9xtD3RK8h6OFiJhTzJE0HZIQtdeTUAGlFh53pAJL6g= X-Received: by 2002:a5d:64ae:0:b0:391:10c5:d1c6 with SMTP id ffacd0b85a97d-3911f72ff44mr5895167f8f.2.1741252786111; Thu, 06 Mar 2025 01:19:46 -0800 (PST) X-Google-Smtp-Source: AGHT+IGgHNDlyxd7gScP5sRIupjVHZHV0IbVTS8wDNRrqJlrNF8ED9HuMeKDsApwMXgdi6IQFHmMpw== X-Received: by 2002:a5d:64ae:0:b0:391:10c5:d1c6 with SMTP id ffacd0b85a97d-3911f72ff44mr5895129f8f.2.1741252785657; Thu, 06 Mar 2025 01:19:45 -0800 (PST) Received: from ?IPV6:2003:cb:c74d:4400:2f98:9b35:6822:ce54? (p200300cbc74d44002f989b356822ce54.dip0.t-ipconnect.de. [2003:cb:c74d:4400:2f98:9b35:6822:ce54]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3912bfdfcb8sm1425864f8f.33.2025.03.06.01.19.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Mar 2025 01:19:45 -0800 (PST) Message-ID: <4a9f102a-60db-475a-a933-975edb2fb1dd@redhat.com> Date: Thu, 6 Mar 2025 10:19:41 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 2/8] mm/huge_memory: add two new (not yet used) functions for folio_split() To: Zi Yan , Hugh Dickins Cc: linux-mm@kvack.org, Andrew Morton , "Kirill A . Shutemov" , "Matthew Wilcox (Oracle)" , Ryan Roberts , Yang Shi , Miaohe Lin , Kefeng Wang , Yu Zhao , John Hubbard , Baolin Wang , linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Kairui Song , Liu Shixin References: <20250226210032.2044041-1-ziy@nvidia.com> <20250226210032.2044041-3-ziy@nvidia.com> <2fae27fe-6e2e-3587-4b68-072118d80cf8@google.com> <238c28cb-ce1c-40f5-ec9e-82c5312f0947@google.com> <43642DB0-17E5-4B3E-9095-665806FE38C5@nvidia.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: <43642DB0-17E5-4B3E-9095-665806FE38C5@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: fyN9h0A3rUMZ56XU8ZZt-jzGoS4cORQb3aGWJkVa24I_1741252786 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: 3EA2220004 X-Stat-Signature: jjgh7war3jwfxxgstfjnc6twy1w34f54 X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1741252789-615484 X-HE-Meta: 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 46qi9w7P VTY+cUUnOosZRGjl6Z5XZRTFihYGKmyIUFSOlpgxDJX9h8MzhzacoVU22kAGBN4RVH5KLRm1XIm0V0+sCG9hPwApDcghiDc7WYEimUzfw/XxGq2fJDGhOyVUxmDlH1UR0ArniO0/0XJ25k8sm9tgsjgF778y2tRv5iJBsANhd0x1EDONIfSER5NyAhD4Bt1hQWkGmfu/U1mWeXcJIapTKe/ljpJSquw4DlYql94fox2cBd7PJQFph3l7z4QX1a+DInbcyZvWMvNybZl1lFyZyF66Tsx8BrSbHgAyy6h6UT1/bBmyP+DG94tK4twPlIuiiJbDZQQcssp9rjOOWscjiM290wQ14nzX8nR39H79D7lklXs84mlHVsEdWEj0gMdKC8awhRWebKUHeOEvtT1KX5/Op3lO4TD/pFStlAqeNr57jQLsun5IljPVoBvMX7DnUB0QB 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 05.03.25 22:08, Zi Yan wrote: > On 5 Mar 2025, at 15:50, Hugh Dickins wrote: > >> On Wed, 5 Mar 2025, Zi Yan wrote: >>> On 4 Mar 2025, at 6:49, Hugh Dickins wrote: >>>> >>>> I think (might be wrong, I'm in a rush) my mods are all to this >>>> "add two new (not yet used) functions for folio_split()" patch: >>>> please merge them in if you agree. >>>> >>>> 1. From source inspection, it looks like a folio_set_order() was missed. >>> >>> Actually no. folio_set_order(folio, new_order) is called multiple times >>> in the for loop above. It is duplicated but not missing. >> >> I was about to disagree with you, when at last I saw that, yes, >> it is doing that on "folio" at the time of setting up "new_folio". >> >> That is confusing: in all other respects, that loop is reading folio >> to set up new_folio. Do you have a reason for doing it there? > > No. I agree your fix is better. Just point out folio_set_order() should > not trigger a bug. > >> >> The transient "nested folio" situation is anomalous either way. >> I'd certainly prefer it to be done at the point where you >> ClearPageCompound when !new_order; but if you think there's an issue >> with racing isolate_migratepages_block() or something like that, which >> your current placement handles better, then please add a line of comment >> both where you do it and where I expected to find it - thanks. > > Sure. I will use your patch unless I find some racing issue. > >> >> (Historically, there was quite a lot of difficulty in getting the order >> of events in __split_huge_page_tail() to be safe: I wonder whether we >> shall see a crop of new weird bugs from these changes. I note that your >> loops advance forwards, whereas the old ones went backwards: but I don't >> have anything to say you're wrong. I think it's mainly a matter of how >> the first tail or two gets handled: which might be why you want to >> folio_set_order(folio, new_order) at the earliest opportunity.) > > I am worried about that too. In addition, in __split_huge_page_tail(), > page refcount is restored right after new tail folio split is done, > whereas I needed to delay them until all new after-split folios > are done, since non-uniform split is iterative and only the after-split > folios NOT containing the split_at page will be released. These > folios are locked and frozen after __split_folio_to_order() like > the original folio. Maybe because there are more such locked frozen > folios than before? What's the general concern here? A frozen folio cannot be referenced and consequently not trusted. For example, if we want to speculatively lookup a folio in the pagecache and find it to be frozen, we'll have to spin (retry) until we find a folio that is unfrozen. While a folio has a refcount of 0, there are no guarantees. It could change its size, it could be freed + reallocated (changed mapping etc) ... So whoever wants to grab a speculative reference -- using folio_try_get() -- must re-verify folio properties after grabbing the speculative reference succeeded. Including whether it is small/large, number of pages, mapping, ... The important part is to unfreeze a folio only once it was fully prepared (e.g., order set, compound pages links to head set up etc). I am not sure if the sequence in which you process folios during a split matters here when doing a split: only that, whatever new folio is unfrozen, is properly initialized. -- Cheers, David / dhildenb