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 24FF2CD8C9F for ; Mon, 8 Jun 2026 14:37:19 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6E7136B0092; Mon, 8 Jun 2026 10:37:18 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 697636B0093; Mon, 8 Jun 2026 10:37:18 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5AD5F6B0095; Mon, 8 Jun 2026 10:37:18 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 4ABE76B0092 for ; Mon, 8 Jun 2026 10:37:18 -0400 (EDT) Received: from smtpin06.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay02.hostedemail.com (Postfix) with ESMTP id C55A612015E for ; Mon, 8 Jun 2026 14:37:17 +0000 (UTC) X-FDA: 84856998114.06.FC8D161 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf04.hostedemail.com (Postfix) with ESMTP id 0F90E40007 for ; Mon, 8 Jun 2026 14:37:15 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=j07VGJdK; spf=pass (imf04.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1780929436; 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=uBr8PiU7vWQLlPrHpDw/6kTJA2t7TuI3TV45DUb6XMk=; b=ewpoiU7XLArUtngyYLdKSNCTSZD6UkJdw8sU1c9diEabJfTgBspkaoENHkM+So8ivOfmoX 9NRIBKF5j7i80GVQzPEa/Iu96WfeFCue1gK+SK34YsKe9muBf25A2/DgnMIxZSvA35bXTR M4ORKMBg9DY6yBC56k4sKgvimPvAmCY= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=j07VGJdK; spf=pass (imf04.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1780929436; b=l0BS833Z2QVgqoyPpBvW5QRCIyzjGQu1IqOmSIXRYrxP5IKrUGO5h+ivjnnDY1hDQfclpz +4/Xqtz69Jf8ASC+PgDZLAihOi93gNudnd4dcwShUWwFLHfOd0A2vS2JIdNwxh+QBtwa0F TEhB/w9AMC+g8J8SdP1IV8xSfEHGZWU= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 74076601E6; Mon, 8 Jun 2026 14:37:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0DFED1F00893; Mon, 8 Jun 2026 14:37:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780929435; bh=uBr8PiU7vWQLlPrHpDw/6kTJA2t7TuI3TV45DUb6XMk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=j07VGJdKbzFDO+1G3fCQcS/gaDMdymxx1YOSKH7X7jb31os3dUjM++/1kZEPnDulh eUlPYtv5XNpiuWfWqR+TUuYJgTZDuC7ngGx9nL7apAYOK2ovAUnsdDUsbFlIZdIYTr /SnezjuEcnGMBpKWcWAg5xrtRgxGaUUEDNUQnzGNO9uRSKgHQIW3LE3ZK9oQz0QxqO V+D9OLBU/P7nLaWPoir+oEXoA8tC1pe6p+DQD4qhFWcbRy2/8c9l3BPGgk0YM++aNk NcFGPalvOvcd6eKR4K8wZLpA+jxg3+w4XI784IDl/o/A5rLQzUNMMFvA9Aq2CMr12m RfVCXpq1tljaQ== Message-ID: Date: Mon, 8 Jun 2026 16:37:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 07/37] mm: thread user_addr through page allocator for cache-friendly zeroing To: Matthew Wilcox Cc: Lorenzo Stoakes , "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, Jason Wang , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Muchun Song , Oscar Salvador , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Hugh Dickins , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Axel Rasmussen , Yuanchu Xie , Wei Xu , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , virtualization@lists.linux.dev, linux-mm@kvack.org, Andrea Arcangeli References: <50d410b47fe3f45327783e05bd306d5eaab75e65.1780906288.git.mst@redhat.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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 0F90E40007 X-Stat-Signature: h5r13b7aex8gjf6jfg5grjgxmon7wdze X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1780929435-279641 X-HE-Meta: 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 H1IMxd92 pTtWTh+X4WFB87g1Plce7JfiBcitQx+Czqhw5teMEpVPU3PtZdjUg3DPklHBNWdxSc2XVjmQh3YjZgb8AgGt7qZSc0BIRhBAWJHLUek7pAhv7E4AQreZWteTWndP/rKzh19PN2LI4e6bpdXi07OCKeRVhTWKxTjLweMf4CPNIWmBkSdOwp0oQRUQ2NGt4AtUAFzqmFjkAwDGsJ0NObs4K5G9BIbzybc2f2DwfKgvFKP48BkufuT7qtIFAH0Q7rWMJg3jFM/pizbFt2I0TLjapy5yvJBGvwNam1PIIGp8RzXCGD3qT+vpUSnCBeC9kAAlXh7mUJAGS+MvzPEvNcLfHcPs5vKyiMMSStJLB58+195DaXtaEKLKNihqhIFTBQkgfnOcx Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/8/26 16:31, Matthew Wilcox wrote: > On Mon, Jun 08, 2026 at 04:26:18PM +0200, David Hildenbrand (Arm) wrote: >> If that means that we would handle __GFP_ZERO consistently in the callers of >> alloc_frozen_pages(), that would also do I guess. We'd still have to pass the >> user address down to some degree, through folio interfaces only at least. > > What I don't understand is how the kernel page allocator needs to know > the user address in order to effectively zero it, but the hypervisor is > able to zero the page without knowing the user address. It feels like > somebody has x86-centric thinking where cache colouring doesn't matter. (not commenting on the icache dache mess we have to drag along) The thing is that with free-page-reporting the memory is already zeroed by the hypervisor as part of discarding that memory previously (e.g., MADV_DONTNEED) and allocating fresh pages on re-access. So it's not a question of "why is the hypervisor zeroing less efficiently", as zeroing is just a side-product of reclaiming that memory in the first place. -- Cheers, David