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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C9700CCD1BC for ; Thu, 23 Oct 2025 07:24:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 243868E0003; Thu, 23 Oct 2025 03:24:36 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1F2BC8E0002; Thu, 23 Oct 2025 03:24:36 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0BB778E0003; Thu, 23 Oct 2025 03:24:36 -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 ED9A38E0002 for ; Thu, 23 Oct 2025 03:24:35 -0400 (EDT) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 9F32C12998B for ; Thu, 23 Oct 2025 07:24:35 +0000 (UTC) X-FDA: 84028541310.12.06DE63B Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf28.hostedemail.com (Postfix) with ESMTP id 1E9E5C0008 for ; Thu, 23 Oct 2025 07:24:32 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=dqojjb2D; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf28.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1761204273; a=rsa-sha256; cv=none; b=eiBO44MfCk2zRCmlKpXaRRqvSi/0x8dQ7GOTD/7AVbYousSMiP/NzKnEGgcoDex5pCC+DD I8TPIQN1M6evF6c6YWF4bwsnfIhSqjvlYv5joCG1wC52SooV+E0lJQtvcF+1dHYwV6yI0J 0wDC2HdFecLtoPo5UMwPEkODgabdJhw= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=dqojjb2D; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf28.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=1761204273; 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=At4MrgAP9F7GQPooz+KssPb3r2AaqOOpWbjQGvPMAWQ=; b=7EOXTlHuca/iPd8aBm+7nb94Du+T4MiRRH1dCJmA42LGGUoK/6+ftpkuIsTbSLC9U6S9JJ ngUAauIWW/8F7MpurKGte1Vd42PYZ8/D1AOtWOrAo7fA4bsWxrrbh5rJ/mmwJS/MK2fsml MPJX/ChWjSTWfv3ivrkCP4HaSHZ9rvw= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1761204272; 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=At4MrgAP9F7GQPooz+KssPb3r2AaqOOpWbjQGvPMAWQ=; b=dqojjb2DnuAZCt76Q/UJRb6fhIVsLrVIkvYyhhqfluMPoUAvOkhs3deY3qpgRyRjqMMPON nB2hUHxssrJxA+mktnPjRq/SxCzJIg5k8U6sJC5CXgS5HKDZ45kUzcL9mRQo98FgjJ7Xpn IElo7fMBjjsyVTI8WxCOBQqWqVbJsQE= 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-300-DCXUaJHNO2qfsVhuIH219Q-1; Thu, 23 Oct 2025 03:24:31 -0400 X-MC-Unique: DCXUaJHNO2qfsVhuIH219Q-1 X-Mimecast-MFC-AGG-ID: DCXUaJHNO2qfsVhuIH219Q_1761204270 Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-42700160169so222237f8f.1 for ; Thu, 23 Oct 2025 00:24:31 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1761204270; x=1761809070; h=content-transfer-encoding:in-reply-to: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=At4MrgAP9F7GQPooz+KssPb3r2AaqOOpWbjQGvPMAWQ=; b=DO5ZAg3WIdgktIeV+B3yy9hk2u4U8mG+kktojm8n48LGbijIADBiBqFiY3ktnXFp88 SpfWDtpYfJwl6GV+WO+1cmQdr1lZ+2vd1jwUFnbytWCJDNOwO0SbaTL2hTU4OlByBswr cP4Z8eMrXt5HMB2jhboRrKNkT/tFmmYMnAS8o8Gk7akhdloZL440QuNjoKmSD5YX6VpO HsJemeaL91aam6XRvxNhi5oogXH5eBP9lz6hYnxG3VIoc8jfKhLx7KwBq8b/Gttiq1cA yZ8xExIyW2lqpZXdW/YonQ1nVvrIA0tv9yvrv5uTNq0oM7XAu5awsIyvtDcCyaD0bZW6 YaLw== X-Forwarded-Encrypted: i=1; AJvYcCV+SjnPHaSRiUZ7+NosUKMkv8jPqcnfDchjuS10paxKXhp7/x3IWJZi+S8Bha6/9FFafFGewQ+O8Q==@kvack.org X-Gm-Message-State: AOJu0Yzcjp51KCEFjuottqwwETDsuTV+7Hh4hKBqC7BtlwLwz57z95pZ KomDRBjzr6He3tTcbHuJIzDEdihAXvCNRXUij5bOfDa+xZPxP7WWv9migjJ45iqTVDHs9nWMPl2 a+qJ16Pbs4ZEU+1vRbuyd9QDqfV9Zpdxca005XDnppWn8bpYBQ7ig X-Gm-Gg: ASbGncugrEP5hwQRc5722vXtotLNtmUWHxWbkD6InaSMzSgyk0TxU1hO5gmOqXonX/1 ujcG4BHpaAf2CJqNDMqrQOOyOkhcreIVDXt0KQeCya3JKAGaDxs3xiLYmc2OqRhOcwJAHlrtI2K Vo7lEuMe3t2PBIfzVsJlTbGzg9zm8p555tGdsyFtZqFN0JKhleyL/v/PqygAWfpjLX3eEpOqRVE ZTv7QC9MQT2MgMVXELugb4NcaYFnqZvBgGxlb4Hp3UEiTLr1N5XAT78ReOiUgPRhwUZD3Hq83xH XSC4GvDrBxwtmseqaIrrzu+VRFf6N7IrTUJ17okk5O63Fs23cqdRRc0FzJDEExD0ObMSRhzX6E1 B62wzKOQDZJ/YNgbPVaMAO9SHLQtTf2k= X-Received: by 2002:a05:6000:4202:b0:426:d82f:889e with SMTP id ffacd0b85a97d-42704d74dc8mr17413744f8f.14.1761204269960; Thu, 23 Oct 2025 00:24:29 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFBeaZeBjNlT5I0rpSARhRSXau88x2Xc7FXWiFhfLb1011+8VdGMBFcPxLi9mgKNY+vLoBXcQ== X-Received: by 2002:a05:6000:4202:b0:426:d82f:889e with SMTP id ffacd0b85a97d-42704d74dc8mr17413724f8f.14.1761204269544; Thu, 23 Oct 2025 00:24:29 -0700 (PDT) Received: from [192.168.3.141] (p57a1af76.dip0.t-ipconnect.de. [87.161.175.118]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-429898ebf82sm2481947f8f.42.2025.10.23.00.24.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Oct 2025 00:24:29 -0700 (PDT) Message-ID: <41f30998-e498-4c33-a4b4-99b9f7339fd7@redhat.com> Date: Thu, 23 Oct 2025 09:24:27 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Possible regression in pin_user_pages_fast() behavior after commit 7ac67301e82f ("ext4: enable large folio for regular file") To: Zhang Yi , Karol Wachowski Cc: tytso@mit.edu, adilger.kernel@dilger.ca, linux-mm@kvack.org, linux-ext4@vger.kernel.org References: <20251020084736.591739-1-karol.wachowski@linux.intel.com> <0fec500c-52ea-473d-b276-826c0f4dd76f@huaweicloud.com> <43cc7217-93bc-4ee6-99d2-83d9b26eb31a@redhat.com> <610d89e2-6970-4924-824b-f27a2424979b@huaweicloud.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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <610d89e2-6970-4924-824b-f27a2424979b@huaweicloud.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: HCDOVOt1gda92la-9H5Q7DAvbaVEJSFssYjVXoZOmxc_1761204270 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 1E9E5C0008 X-Stat-Signature: ttg3bm4ef8aobtor6bxjfuhfewryhs5t X-HE-Tag: 1761204272-751311 X-HE-Meta: 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 N5YxQwPK 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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: >> __split_huge_pmd_locked() contains that handling. >> >> We have to do that because we did not preallocate a page table we can just throw in. >> >> We could do that on this path instead: remap the PMD to be mapped by a PTE table. We'd have to preallocate a page table. >> >> That would avoid the do_pte_missing() below for such faults. >> >> that could be done later on top of this fix. > > Yeah, thank you for the explanation! I have another question, just curious. > Why do we have to fall back to installing the PTE table instead of creating > a new anonymous large folio (2M) and setting a new leaf huge PMD? Primarily because it would waste more memory for various use cases, on a factor of 512. > >> >>>    |     handle_pte_fault()  // >>>    |      do_pte_missing() >>>    |       do_fault() >>>    |        do_read_fault() //FAULT_FLAG_WRITE is not set >>>    |         finish_fault() >>>    |          do_set_pmd() //install leaf pmd again, I think this is wrong!!! >>>    |      do_wp_page() //copy private anno pages >>>    <-    goto retry >>> >>> Due to an incorrectly large PMD set in do_read_fault(), follow_pmd_mask() >>> always returns -EMLINK, causing an infinite loop. Under normal >>> circumstances, I suppose it should fall back to do_wp_page(), which installs >>> the anonymous page into the PTE. This is also why mappings smaller than 2MB >>> do not trigger this issue. In addition, if you add FOLL_WRITE when calling >>> pin_user_pages_fast(), it also will not trigger this issue becasue do_fault() >>> will call do_cow_fault() to create anonymous pages. >>> >>> The above is my analysis, and I tried the following fix, which can solve >>> the issue (I haven't done a full test yet). But I am not expert in the MM >>> field, I might have missed something, and this needs to be reviewed by MM >>> experts. >>> >>> Best regards, >>> Yi. >>> >>> diff --git a/mm/memory.c b/mm/memory.c >>> index 74b45e258323..64846a030a5b 100644 >>> --- a/mm/memory.c >>> +++ b/mm/memory.c >>> @@ -5342,6 +5342,10 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio, struct page *pa >>>       if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER)) >>>           return ret; >>> >>> +    if (vmf->flags & (FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE) && >>> +        !pmd_write(*vmf->pmd)) >>> +        return ret; >> >> Likely we would want to make this depend on is_cow_mapping(). >> >> /* >>  * We're about to trigger CoW, so never map it through a PMD. >>  */ >> if (is_cow_mapping(vma->vm_flags && >>     vmf->flags & (FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE))) >>     return ret; >> > > Sure, adding a cow check would be better. I will send out an official patch. Thanks! -- Cheers David / dhildenb