From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CD0C836B920; Tue, 29 Sep 2026 07:36:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790667406; cv=none; b=CHcMYf04r+/C/RmlWMNbtvYewAO4dnBIAS8OvzIH7zjOKynRbnL368TG3QmcZ/ryNJ3GN+E3YJfDHZ9hy/ZDPm51Ve7WZN8iC5nJFZNyWgnddykv43Fu3iTiKdzvz1HmDw4pG5jxhxfsI1tTcMjdAbjqlbaYlDP+e491hzlmekI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790667406; c=relaxed/simple; bh=aLSR3jeN6SEnb6pKT6saVvqm/ATzFiwB7UR5fQfZciM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=u46BOokXUb9ir/GicIZz0OnpwgWRKxnRmVxRtaqXzZn4RmVJjq9UM7W54tGeVJLQKMul817JnkSfaxBENr/bgrU/+YvT4GTDkF5Ng+xR8QJ+1bqkyelXie+r0sRCRR0cZ/5s+U3qnzhkHAx4isY2GCLCLaO7Gx7ISWuRjuhIcKI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IimBV9tX; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="IimBV9tX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F27901F000FF; Tue, 29 Sep 2026 07:36:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790667405; bh=N4ktdpi1f+/KDUD6L3UXr89sslU38XOXuJkv+riiaEg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=IimBV9tXab1BYBvx21vk5zYso+7dCfqv09ZfPCCNxIZBCG0qD2CSZiCF92zrEcDAh TZg4vfypokm6PuGRQZHu1ZzssiOGuX0/iFqcx9FOkfesKhn3Lp2cKO9itGJ/PUIuAA Gvh3WIqS2aoJaEgiCtSn1KvbcMaM252im82unuIUQ2IhlZTmJBd3WBfBuQadjWxKY9 c6G/sp2lpauOWFZrtfhL/6RLZBIsRzZ2x8JV6Wo9bPNjkwNh/wzxFrcUHIdAi6RAGW Cet9Rh+AYl+P53tJDy0E7ZdskiaxsvWxU2X2ECcv/49QACR19eLfXC26MZhuDzVC2T Lw0OFJeLZGfpw== Message-ID: <1b542015-8e5a-41af-9e98-9810333e6725@kernel.org> Date: Tue, 29 Sep 2026 09:36:39 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 07/12] mm/sparse-vmemmap: switch device DAX to shared tail vmemmap pages To: Muchun Song , Andrew Morton , Oscar Salvador , Madhavan Srinivasan , Michael Ellerman , Jonathan Corbet Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-doc@vger.kernel.org, Muchun Song , Lorenzo Stoakes , Mike Rapoport , Qi Zheng , Nicholas Piggin , Christophe Leroy , Randy Dunlap , Lance Yang References: <20260927025441.741633-1-songmuchun@bytedance.com> <20260927025441.741633-8-songmuchun@bytedance.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: <20260927025441.741633-8-songmuchun@bytedance.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/27/26 04:54, Muchun Song wrote: > HugeTLB vmemmap optimization now uses per-zone shared tail vmemmap pages. > Device DAX has not been switched to that mechanism yet. > > Switch device DAX to vmemmap_shared_tail_page() as well. This aligns DAX > with HugeTLB by using the common per-zone shared tail vmemmap page. > > The optimization is enabled only for DEV-DAX through pgmap->vmemmap_shift, > which supplies the compound page order recorded in section metadata before > vmemmap population. Unlike FS-DAX, DEV-DAX does not modify tail struct > pages, so sharing them is safe. > > Since the shared tail page can now back ZONE_DEVICE vmemmap mappings, > initialize its entries with PG_reserved for device zones. Also skip > poisoning vmemmap-optimizable sections while their struct pages may be > shared. > > Signed-off-by: Muchun Song > Acked-by: Qi Zheng > --- > v3: > - Move device_zone() after the definition of NODE_DATA() to fix > non-NUMA builds. > - Update the commit message to describe the compound page order stored > in section metadata > - Collect Acked-by from Qi Zheng > > v2: > - Explain why sharing tail vmemmap pages is safe for DEV-DAX > (suggested by Qi Zheng) > --- [...] > - > static int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn, > unsigned long start, > unsigned long end, int node, > @@ -551,21 +536,18 @@ static int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn, > pte_t *pte; > int rc; > unsigned long flags = VMEMMAP_POPULATE_DAX; > + struct page *page; > + unsigned int order = pfn_to_section_compound_order(start_pfn); const and all the way to the top. I did wonder about the poisoning change ... because the memmap usually gets initialized once the memory section gets moved to a zone. SO now I'm a bit confused about the ordering of events :) -- Cheers, David