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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C8C53FF8867 for ; Mon, 27 Apr 2026 20:33:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=0zilGkucIvAKI2C1BINewP5ngC2cVQqU9MCjENDL+F0=; b=DIZjfBDjxYEKgm04+KoSA+qS8H LDpyTe+82FJu/zfl/7FLzJAwY6nNtBJ899JCRsscdhlGeanVfNLbJ2uoFzMKoyzdWOxVFnt3AeCsC i7PVyF8DSYtBnUYSc3OFuH63U13QaQaB/ay87/+iaNgQ2mrI+4GJkaBfK5mY/RKgUc0+9fNaag6Yi wbaRh9LU0I0zq66YYDEXy9LCD+/Y1biCK7ifYJj1PQojahxbAdyvUgLuwukAw483lyvpyoI/2eLMA EXjV40jFd2XOwKntj0VZsu71NC07SdTcMZlnjOAvVx7NAQMPAjruxv5PtSbH3Rd2P0JBswqGBMye5 XUIMmgNw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1wHSda-0000000085I-1B2R; Mon, 27 Apr 2026 20:33:02 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1wHSdX-0000000084u-3VU4 for linux-arm-kernel@lists.infradead.org; Mon, 27 Apr 2026 20:33:00 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id DC5F642B8C; Mon, 27 Apr 2026 20:32:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 907F7C19425; Mon, 27 Apr 2026 20:32:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777321978; bh=AYegFMHP0FdsG4kub/LfFJkX3yPMbTV5RSbToEya7YE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=CPpGeZqUUq4NeHLjr8Y6gHhQ05OKQLcZ0ZJVizuxBD/hnh6paiIYrIaKnVuuk0EWe uYc3mVuCWJhlzjC04W4vgsZ2z+vmdwMvbLJyFiFcyeCY/Uqq8FIQ7ITfxECAGUtWnT 445TSQd8UPwBSkkeHWgDEd08Z5PuIQaQrtrInshYoGmv/n+R8hYzz6uxvVaiH5hL4n tAUtIiwsnIUACypW2QAIXakl9lt0s90+wFQj1nY9viO0zXAtVev6mYsQGHg8yzH+9V LLCz45rzypGCC1pYmnOEA0N1vkqM7F3g1RBDqMXXhebeC5qq5sDX5noJ6G/U/bdIpd ydqaY9P//sj0g== Message-ID: <67a655e3-fa23-4d2a-9685-14e6221d5d26@kernel.org> Date: Mon, 27 Apr 2026 22:32:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RESEND] Re: [PATCH RFC v3 4/4] mm: add PMD-level huge page support for remap_pfn_range() To: Yin Tirui , lorenzo.stoakes@oracle.com Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, willy@infradead.org, jgross@suse.com, catalin.marinas@arm.com, will@kernel.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, luto@kernel.org, peterz@infradead.org, akpm@linux-foundation.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, anshuman.khandual@arm.com, rmclure@linux.ibm.com, kevin.brodsky@arm.com, apopple@nvidia.com, ajd@linux.ibm.com, pasha.tatashin@soleen.com, bhe@redhat.com, thuth@redhat.com, coxu@redhat.com, dan.j.williams@intel.com, yu-cheng.yu@intel.com, baolu.lu@linux.intel.com, conor.dooley@microchip.com, Jonathan.Cameron@huawei.com, riel@surriel.com, wangkefeng.wang@huawei.com, chenjun102@huawei.com References: <20260228070906.1418911-1-yintirui@huawei.com> <20260228070906.1418911-5-yintirui@huawei.com> <9886b2c6-5516-4be8-ac31-db3133455af2@kernel.org> <39dac497-220c-4e71-9d3e-d9cf32357400@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+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: <39dac497-220c-4e71-9d3e-d9cf32357400@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260427_133259_927787_54FE9B42 X-CRM114-Status: GOOD ( 17.69 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org >>> + pte_t entry; >>> + >>> + if (!pmd_special(old_pmd)) { >> >> If you are using pmd_special(), you are doing something wrong. >> >> Hint: vm_normal_page_pmd() is usually what you want. > > Spot on. > > While looking into applying vm_normal_folio_pmd() here to avoid the > magical VMA checks, I realized that both __split_huge_pmd_locked() and > copy_huge_pmd() currently suffer from the same !vma_is_anonymous(vma) > top-level entanglement. Yes, that code is an absolute mess. > I think these functions could benefit from a > structural refactoring similar to what Lorenzo is currently doing in > zap_huge_pmd(). > > My idea is to flatten both functions into a pmd_present()-driven > decision tree: Likely similar to how we handle PTEs. > 1. Branch strictly on pmd_present(). > 2. For present PMDs, use vm_normal_folio_pmd() as the single source of > truth. > 3. If !folio (and not a huge zero page), it cleanly identifies special > mappings (like PFNMAPs) without relying on vma_is_special_huge(). We can > handle the split/copy directly and return early. > 4. Otherwise, proceed with the normal Anon/File THP logic, or handle > non-present migration entries in the !pmd_present() branch. Yes, that sounds about right. > > I have drafted two preparation patches demonstrating this approach and > appended the diffs at the end of this email. Does this direction look > reasonable to you? If so, I will iron out the implementation details and > include these refactoring patches in my upcoming v4 series. > Yes, sounds like nice cleanups. Maybe the code could then benefit from moving the present vs. non-present handling into separate functions? Just a thought. -- Cheers, David