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 37214C54E55 for ; Thu, 7 Mar 2024 09:20:24 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B26046B0136; Thu, 7 Mar 2024 04:20:23 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id AD4AF6B0137; Thu, 7 Mar 2024 04:20:23 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 927DF6B0138; Thu, 7 Mar 2024 04:20:23 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 82D776B0136 for ; Thu, 7 Mar 2024 04:20:23 -0500 (EST) Received: from smtpin22.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 4DE27A10A3 for ; Thu, 7 Mar 2024 09:20:23 +0000 (UTC) X-FDA: 81869697126.22.BB059DE Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf20.hostedemail.com (Postfix) with ESMTP id 149C71C0011 for ; Thu, 7 Mar 2024 09:20:20 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=C1xyaHoX; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf20.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=1709803221; 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=TThX1qPWJJo2eN4PvOiwI3uhBp26oyxkiGL+YBlZUKY=; b=FMV68C9wGBMt7nSqsOUgav2pt7DYkguvmG1ilQPr0Qgwpz+7tcyf1BPiL2CcsWszMFdbvf qXI24w6gzPAkah1Gthmmtp3SSP1IT3v8Wp14bEMqqixAfrpdQrLvb45gdDFWbMcZflMjDp DHwW7hO/BnabgChidgVBUiWctKmBjdA= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=C1xyaHoX; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf20.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=1709803221; a=rsa-sha256; cv=none; b=n2Y04IXELR3Epng1pMZ1ypIPHKbl7sLaUEKSSt7IMoKhfA+COk0z7ajXBs/40aPAQvyU9v x5A2kvZ7Kv2z0zH+nx5zQYqUTBQqK3mqhxnTVDP6SjpgDXEYvvvwsdMmu3IsKn1P2c2hxI 742XhJdVT1yDF891AYhrKf/I8FqQqgQ= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1709803220; 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=TThX1qPWJJo2eN4PvOiwI3uhBp26oyxkiGL+YBlZUKY=; b=C1xyaHoXVRyA1o5bcHPtLUBmBFT1EWkHbifI/0sooYfF/vB0Ze6YcEAMOaZJi1hHRqdf1V JjEiC6hN5gKKzrcdTrssOIPJral3FzPq44rGIlocrn5+6gYoF/VpivhQGS3LTYwuruaOYF MOhzSsRffOA8x/ORRYVPB3sEPuq9WV8= 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-393-GoLjSZaSPqKUeKjb0coLxg-1; Thu, 07 Mar 2024 04:20:18 -0500 X-MC-Unique: GoLjSZaSPqKUeKjb0coLxg-1 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-412e0abdbf1so5070355e9.3 for ; Thu, 07 Mar 2024 01:20:18 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1709803217; x=1710408017; h=content-transfer-encoding:in-reply-to:organization:autocrypt:from :references:cc:to:content-language:subject:user-agent:mime-version :date:message-id:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=TThX1qPWJJo2eN4PvOiwI3uhBp26oyxkiGL+YBlZUKY=; b=wVcmhLacoZMP6RmggxBHegtUlP2p0RyfAVqAvjgqSWSyjuN0/D9cTEii71ainUrhTk vj1DDth4exD2VislZ7sK0/KNBbeh/Qfj/5pxdH31R+B731yRZ1wXhaZzaYXQovLV6aN3 3fnlH3B6w+u99+GdcJCSmvOn1MnUcrRVMloGRVHReAH+CgYztQqVpJAVRqEhNenSpRE0 +Hv892+hqMySjKsmb+/6WsZOwOMSlTC1y9y08kxfPMcZlEkM1R9F4a2Ldul1JL3k7tJ3 gqIK6I7SeBuwKeSoN650fuuEWbCtMlUjBKz1WyW1RetX7TTi6/V11XafK1Qs0PCZl85+ mhdQ== X-Gm-Message-State: AOJu0YzRZ8idAoLfPAbmNWBegP8GX76F20ce9ZE4uT2GRimoG1//LC6m bNsGlW7bZfgy0gIrRc5xWkK8Y0LrjPR6aEN+oQuflChH7DBFmkJpbse6sj8PCm6rEWU8wx5gliH wBowYytBKRWgmkIApRclyhWE/2YPvhzRyYmmhQBKO8k0BtVOaGKg/5EDj X-Received: by 2002:a05:600c:474d:b0:412:b8fd:2dd4 with SMTP id w13-20020a05600c474d00b00412b8fd2dd4mr12302007wmo.17.1709803217200; Thu, 07 Mar 2024 01:20:17 -0800 (PST) X-Google-Smtp-Source: AGHT+IGX4zvfMsmA6F6yOhk3R4BBRq0JAUd5lf+pBmJqxdGMmKqR7V7YMwJGCHlsJz2+rbTik14Myg== X-Received: by 2002:a05:600c:474d:b0:412:b8fd:2dd4 with SMTP id w13-20020a05600c474d00b00412b8fd2dd4mr12301992wmo.17.1709803216737; Thu, 07 Mar 2024 01:20:16 -0800 (PST) Received: from ?IPV6:2003:cb:c74d:6400:4867:4ed0:9726:a0c9? (p200300cbc74d640048674ed09726a0c9.dip0.t-ipconnect.de. [2003:cb:c74d:6400:4867:4ed0:9726:a0c9]) by smtp.gmail.com with ESMTPSA id bv16-20020a0560001f1000b0033e0523b829sm20264405wrb.13.2024.03.07.01.20.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 Mar 2024 01:20:16 -0800 (PST) Message-ID: Date: Thu, 7 Mar 2024 10:20:15 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/5] Remove some races around folio_test_hugetlb To: Matthew Wilcox Cc: linux-mm@kvack.org, Oscar Salvador References: <20240301214712.2853147-1-willy@infradead.org> <52599fd8-76dc-4d8f-b9f2-78146fc7a518@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: 7bit X-Rspamd-Queue-Id: 149C71C0011 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: uwsjup1qbde8f1fjbay8713uqw3ap1j9 X-HE-Tag: 1709803220-411957 X-HE-Meta: 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 gOiGBQAh IIJlPqrZcOl+fUwhWIYGYw2Y/bOkl1Y+3mdBKVtSdIUD32/4Pvp/KncZQAqI/GLXMQNeTDzUUT8b8eIT28jNOwDEUm5wDmzFEpEOyq186mfh/PP2csZLg6qDn7gzx3V+yn6vr0RQJy/lBEnHIDHIpascT5oN79FN2lVwfLyO7cvJt4OYsINd4kZFp+QeXqzr3lG1fI7RWkEqjctrBSZdKjj+6tg== 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: >>> >>> IOW: >>> >>> word page0 page1 >>> 0 flags flags >>> 1 lru.next head >>> 2 lru.prev entire_mapcount + gap >>> 3 mapping nr_pages_mapped + gap / hugetlb_id >>> 4 index pincount + nr_pages >>> 5 private unused >>> 6 mapcount+refcount mapcount+refcount(0) >>> 7 memcg_data - >>> >>> or on 32-bit >>> >>> word page0 page1 >>> 0 flags flags >>> 1 lru.next head >>> 2 lru.prev entire_mapcount >>> 3 mapping nr_pages_mapped / hugetlb_id >> >> ^ In the worst case, I think, nr_pages_mapped with a lot of entire mappings >> could end up matching hugetlb_id. We add a large value to nr_pages_mapped >> every time we add an entire mapping ... (not sure if that could currently be >> a problem with many entire mappings of a large folio) > > My understanding was that nr_pages_mapped was incremented by one for > each page which has a non-zero mapcount. It was also incremented by > ENTIRELY_MAPPED the first time that we increment ->entire_mapcount. > As such, I don't think entire_mapcount can get the top bit set. Right, I misremembered! > >> >>> 4 index pincount >>> 5 private unused >>> 6 mapcount mapcount >>> 7 refcount refcount >>> 8 memcg_data - >>> 9+ virtual? last_cpupid? whatever >>> >>> Does this fit with your plans? >> >> For the total mapcount this would do (and it would be better), but the >> layout gets a bit "sparse" on 64bit that way, which will end up being >> problematic for some other stuff I might want to put in there. >> >> Not that we have to resolve that now, just bringing it up, that maybe we can >> do better right away :) > > How about this layout? > > @@ -350,8 +350,13 @@ struct folio { > unsigned long _head_1; > unsigned long _folio_avail; > /* public: */ > - atomic_t _entire_mapcount; > - atomic_t _nr_pages_mapped; > + union { > + unsigned long _hugetlb_id; > + struct { > + atomic_t _entire_mapcount; > + atomic_t _nr_pages_mapped; > + }; > + }; > atomic_t _pincount; > #ifdef CONFIG_64BIT > unsigned int _folio_nr_pages; > > That keeps _folio_avail as, well, available. It puts _hugetlb_id in > the same bits as ->mapping. It continues to leave ->private unused > on 64-bit. I think this does everything we want? _entire_mapcount is (still) used for hugetlb folios. With the total mapcount in place, I was thinking about renaming it to "_pmd_mapcount" and stop using it for hugetlb folios, just like we'd not be using _nr_pages_mapped for hugetlb folios. [I also thought about moving the _pmd_mapcount to another subpage, where we'd also have a _pud_mapcount in the future; but again, stuff for the future] Until then, wouldn't _hugetlb_id be problematic here? [I could move _entire_mapcount/_pmd_mapcount later I guess] -- Cheers, David / dhildenb