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 06ECA472F87 for ; Mon, 19 Oct 2026 12:18:51 +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=1792412332; cv=none; b=mNh/zUqW2lko81s9zW6KNvGXnes7JEa3tkJvV4ThEzy33EngUi6iX25Di21vXExSj81p6MPZuLcn6Z8GQ7r0C2FG+fzshiF0Cyv+JSrBj1fkmJF/u5hIM4u9NbQPUidurEm5FMlNQX3ZhHUFODNzKix88ssJNX4xtEMlWQEOeWo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792412332; c=relaxed/simple; bh=8XYz6JvVxvGOfYch9mnM99v0BtGkYb4LfNopepeACV0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=h8KXBlOK6yELt6DpwB84/c9B5/xBXkoJVOxRiOpzTEMdZAgzM8VZjR/PhcqeXoW1kA7XCfZsO7AixncgIX1zOkuPObeF7GApJxdC8wRYbGkrmtQx0rD88RjVzrX5Tm+2xdj1sUwp3VEhmx8giC7erdDvPm9+HUGVfRID8hMORmY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=h6xAxbdm; 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="h6xAxbdm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D680A1F000C5; Mon, 19 Oct 2026 12:18:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792412331; bh=3u1HT8y1funuQIDNMJr/wgEzzPt99e6m6N2aOvfKG08=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=h6xAxbdmmRscN8KquCBh3c6cUyJOHdsi8Scc3e+32LcZ05UCJIk2rlprgoWJs+2m7 0bbmfCu5AuKSybaZ3pZIZNfRwqMOMm+pfFnLgQ5fhPk/SMq7iKYjSH0ozmDGbVEbEC 3Jc6qBcykfLGMYyQtIITtGNZRD1LB5w0ozsLXW/TAYlDQpFo984i6TsNwmwYo9khM5 Xd19hB3d3tevBat6VxnYCj4kXV8+r/jWVpRzk5311pcb7U7EJXXYkwyuRpAZpgeXpj uYEzNQj2Au+AhzmpWu9N6g6dLdV3K3nybdiJXsp/Bivh19oRFo3Lnlh4xYgbvz+LQX ihR6T1abdhYRA== Message-ID: <1eff2f1a-b7bc-4541-82f0-9836d0a5db5c@kernel.org> Date: Mon, 19 Oct 2026 14:18:47 +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 0/5] mm: hugetlb: add CMA support for PMD-sized page To: "Jose A. Perez de Azpillaga" , Muchun Song Cc: Qi Zheng , Qi Zheng , osalvador@suse.de, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <4a7ad39d-fee6-4390-beff-d40ecf49cbdc@bytedance.com> <988249c7-abf0-4f4f-9386-27e835a4d2de@gmail.com> <1385f5a1-b842-45e6-8986-fec4123037f1@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: <1385f5a1-b842-45e6-8986-fec4123037f1@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/19/26 11:17, Jose A. Perez de Azpillaga wrote: > On 10/19/26 10:43 AM, Muchun Song wrote: >> >> >>> >>> >>> wouldn't a shared pool still be sized and aligned for 1G? then the 2M >>> headroom stays a multiple of 1G and the 1G-aligned reservation can still >>> fail, which is what the series is trying to avoid. >> >> If we decide to use a shared pool, I think the current alignment strategy >> should be adapted as well, it should be changed to align with the minimal >> acquirement, like 2M. >> >> For example, if a user reserves 1G+2M through hugetlb_cma, then the memory >> reserved by the pool is also 1G+2M, except that the starting address needs >> to be aligned to the largest gigantic page (1G). Therefore, this pool is >> suitable for both 1GB and 2MB allocation. The only problem I see with a >> shared pool is that it may not support mixed-use scenarios very well. >> >> What do you think? > > makes sense to me. existing hugetlb_cma= users with WM pages would get > mixed use without asking for it though. Yeah, my intuition tells me that having 1 allocation size per CMA area might be cleaner. Assume you allocate 512 2 MiB hugetlb folios. You'd think that you would then be able to allocate 1 GiB hugetlb folio less. But that's not guaranteed, as CMA might just fallback to other areas fairly easily. If someone wants to convert from 1 GiB to 512 x 2MiB, I think the demotion interface allows for that. -- Cheers, David