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 18AB8C8303C for ; Tue, 8 Jul 2025 09:02:44 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 951256B0318; Tue, 8 Jul 2025 05:02:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9284B6B0319; Tue, 8 Jul 2025 05:02:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7F01F6B031A; Tue, 8 Jul 2025 05:02:43 -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 6D94B6B0318 for ; Tue, 8 Jul 2025 05:02:43 -0400 (EDT) Received: from smtpin29.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 0A4F61A049C for ; Tue, 8 Jul 2025 09:02:43 +0000 (UTC) X-FDA: 83640507006.29.77CB955 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 8ABD310000E for ; Tue, 8 Jul 2025 09:02:40 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=YPpa9zOb; 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=1751965360; 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=kcqD2oH4KnoupLtw/H9HIDrbwYpbL3NMdx+chRH/ZA4=; b=FUyWA6i9YXI7jC15gLwflCWfjL3+izCzUqi+BaJhzQqs8+K0fJqUFhVhy06lypXwV5RoTu ZYTm6qUR69UaikqAPkOp6H0PuFZZPM+0Ci6TEN/Xo8g1thbTt78M4OO28asQ6V1zKne9Kx A7yxB3qAfGgwH2AEA7/KamNEO1pCbUM= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1751965360; a=rsa-sha256; cv=none; b=ap00Xu4oAqDX96waQgNhyAQHeHrxjM7F0usuyJkMuwFscHhZiR0jpz14Coq9qxWhddHsFX efSzKvkc7LSIRrOfmxXLLgEaEzWPpFdGfM98g37AsfxexM0plYaGRXPB91ObaUuWQGxmWy 9V0iOC432JZoXAmj8jffJT5t5VlHaf4= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=YPpa9zOb; 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=1751965360; 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=kcqD2oH4KnoupLtw/H9HIDrbwYpbL3NMdx+chRH/ZA4=; b=YPpa9zObq9WEuhXQfcVBtCyOpXsSPLXqkZZdb5lUYfnO96tULZ5uzPE7lNLFgFcc8sCle0 tMZpX/9iknDtqZROxA/5cIKidaV29f19XyoeQUV2OcHg+G8KlrB0KJktm0qUXEQgJHZMS4 FF1+W9z2guj+V5JPZgSrgHjR7O46V5w= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-198-VPWyXEMtND6-Cs5n2AR4AA-1; Tue, 08 Jul 2025 05:02:38 -0400 X-MC-Unique: VPWyXEMtND6-Cs5n2AR4AA-1 X-Mimecast-MFC-AGG-ID: VPWyXEMtND6-Cs5n2AR4AA_1751965357 Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-3a6df0c67a6so2317799f8f.3 for ; Tue, 08 Jul 2025 02:02:38 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1751965357; x=1752570157; 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=kcqD2oH4KnoupLtw/H9HIDrbwYpbL3NMdx+chRH/ZA4=; b=WIvsa++9gW/jusHsadR5Wj+Yh4pku9Zm0sOycPlL59Oe1+VErOBf9jJ9krlBWtwpHK 5gmecbU56oTVpFptita0hgajwEUYEhgHhD9b4eZU3xHWmdenbboJk1hICH2BZtFdABp0 aPBzRXcd7Bfke40BcYY0sG6iyOsUPorWVrOJMelozjQYko4AiYGNubKak38M0/a+EeU7 KKmG5JD2I42WVQYXqRe4fS340IUAVraF/OtnSi76UvNXJTTcCW2MQNv6vbUWoiqP0Yvp SpjY98U+hhWT3Jyp7iURRiVLgWO7G9V4kDbNoHaDUIWJHDM1b1EutaCUTksIdk7bN0H7 4+mw== X-Forwarded-Encrypted: i=1; AJvYcCWRzdse9vcn0xvhWLYArplUzUQ/gBNCJHkKcjE4yYKzIKW/c6+oNX9OzcsDRPvWjA7pIImC1E2zaw==@kvack.org X-Gm-Message-State: AOJu0YwbFTrWBrQCbetsYPxh0fOiaaA5RLdvBcmLAP6Lk8WIrJkki9Xr MBmDhb/HRoTQw6yERSdPGCAgkmahqNdU9UmzkY9cGMINthPSqfsLKjJD28eOBFX9xQ6yLi3oxTT LdsCWb/iPYAHveDbPckku6JuxPqgJ39+1zC4ssuOulb+9I7YM0h3f X-Gm-Gg: ASbGncv/S3d7ec15NPKRvrBG+mSI+az32AasmHSEb9j4BkPFXSOTz40039pB3jShG34 4M0FWnbXVn8gCRnLqP5+XRJ9bPU6BuHK848UR9RjlBEse03TKz1v0xUi6eO59f2V5LgwsFvrkC3 3dSrGrb/P41ZQdMbL37lIcYYg7HHJdSMfANzAeID3aCcXF+/YaJ04xgjpeCWzK7CS0ZsjybMo+s MaH4ThJU5LvrdCgRUWvLXGDcdFasOkf/2DlL47MyEPfzeLROxxn5b4U6DuGPCXWE3DDrCEDVctM ac1LxNMpb0oXMla5VUWkg5HrVaXCxBi5kLRmpbSipGWZPZSDRkqw8GGuyrWrBBrZ1TpcDAqpsPO Vf2Zo0/WKBUUrt4h2ERjFM1XOFYECVJN8EPlxo1sHhXeGKDhsNQ== X-Received: by 2002:a05:6000:4a0e:b0:3a6:f2d7:e22b with SMTP id ffacd0b85a97d-3b4970131d6mr10360202f8f.18.1751965357205; Tue, 08 Jul 2025 02:02:37 -0700 (PDT) X-Google-Smtp-Source: AGHT+IH59Q89KB29sNtWTuy+Lnb60jxQ9SnJGY1Q46W5H+PBdpYZf1r953ypo/zQt9WGDDGBVcsxhw== X-Received: by 2002:a05:6000:4a0e:b0:3a6:f2d7:e22b with SMTP id ffacd0b85a97d-3b4970131d6mr10360177f8f.18.1751965356641; Tue, 08 Jul 2025 02:02:36 -0700 (PDT) Received: from ?IPV6:2003:d8:2f1a:f500:4346:f17c:2bde:808c? (p200300d82f1af5004346f17c2bde808c.dip0.t-ipconnect.de. [2003:d8:2f1a:f500:4346:f17c:2bde:808c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b47030ba48sm12559374f8f.13.2025.07.08.02.02.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Jul 2025 02:02:36 -0700 (PDT) Message-ID: <02ee908f-6cd6-4327-a931-8c8747f29354@redhat.com> Date: Tue, 8 Jul 2025 11:02:35 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 mm-new] mm: check if folio has valid mapcount before folio_test_{anon,ksm}() when necessary To: Harry Yoo Cc: Andrew Morton , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Christoph Lameter , David Rientjes , Matthew Wilcox , linux-mm@kvack.org References: <20250707120740.4413-1-harry.yoo@oracle.com> <6716889f-00c1-44db-a7e3-c58a68dcd6ae@redhat.com> <77384767-f821-4736-940b-051664922c8c@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-MFC-PROC-ID: 1ZbOUkmAlZDj6oHwe4AirlZVG7wQ8Y7U8Oje4WZ1WM8_1751965357 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 8ABD310000E X-Stat-Signature: phogpob5eo8isc3p1betphonws3aa4ab X-HE-Tag: 1751965360-634670 X-HE-Meta: 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 SHYR9pdZ 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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 08.07.25 10:56, Harry Yoo wrote: > On Tue, Jul 08, 2025 at 10:32:44AM +0200, David Hildenbrand wrote: >> On 08.07.25 10:30, Harry Yoo wrote: >>> On Tue, Jul 08, 2025 at 10:07:26AM +0200, David Hildenbrand wrote: >>>>> if (folio_test_anon(folio)) { >>>>> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h >>>>> index 970600d79dac..00ba2c8b221e 100644 >>>>> --- a/include/linux/page-flags.h >>>>> +++ b/include/linux/page-flags.h >>>>> @@ -706,12 +706,15 @@ PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted) >>>>> * address_space which maps the folio from disk; whereas "folio_mapped" >>>>> * refers to user virtual address space into which the folio is mapped. >>>>> * >>>>> - * For slab pages, since slab reuses the bits in struct page to store its >>>>> - * internal states, the folio->mapping does not exist as such, nor do >>>>> - * these flags below. So in order to avoid testing non-existent bits, >>>>> - * please make sure that folio_test_slab(folio) actually evaluates to >>>>> - * false before calling the following functions (e.g., folio_test_anon). >>>>> - * See mm/slab.h. >>>>> + * For certain typed pages like slabs, since they reuse bits in struct page >>>>> + * to store internal states, folio->mapping does not point to a valid >>>>> + * mapping, nor do these flags exist. To avoid testing non-existent bits, >>>>> + * make sure folio_has_mapcount() actually evaluates to true before calling >>>>> + * the following functions (e.g., folio_test_anon). >>>>> + * >>>>> + * The folio_has_mapcount() check can be skipped if the folio is mapped >>>>> + * to userspace, since a folio with !folio_has_mapcount() cannot be mapped >>>>> + * to userspace at all. >>>>> */ >>>>> #define FOLIO_MAPPING_ANON 0x1 >>>>> #define FOLIO_MAPPING_ANON_KSM 0x2 >>>>> @@ -1092,6 +1095,11 @@ static inline bool PageHuge(const struct page *page) >>>>> return folio_test_hugetlb(page_folio(page)); >>>>> } >>>>> +static inline bool folio_has_mapcount(const struct folio *folio) >>>>> +{ >>>>> + return !page_has_type(&folio->page) || folio_test_hugetlb(folio); >>>>> +} >>>>> + >>>> >>>> I don't like the naming. >>> >>> I don't like it either, but I couldn't come up with a better name :( >>> >>>> The thing is, in the future only folios will have a mapcount. >>> >>> Agreed. >>> >>>> Asking whether a folio has a mapcount is asking the wrong question. >>> >>> Agreed. >>> >>>> It's rather, that we want to reject *pages* early, and not cast them to the >>>> folio in the first place. >>> >>> Totally agreed. >>> >>> But that's the future, and we're not there yet. >>> What should we do now? >> >> Check before converting from page to folio in stable_page_flags() and leave >> folio_expected_ref_count() alone. In folio_expected_ref_count() it's a >> sanity check that should never happen. > > TBH it wasn't clear when the page-to-folio conversion should be > rejected... (I can't just change page_folio() to reject that, right now) Yes, willy's plan is to make page_folio() fail later. For now, we can just do racy checks ahead of time (kpagecount code is inherently racy). -- Cheers, David / dhildenb