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 603183ECBE3; Tue, 9 Jun 2026 08:12:15 +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=1780992736; cv=none; b=YCcWvY4mb+oH5TfEuURhg0bAimRhWxgd8X9AbIDJCQKSyYI1xI7G0Euh7cSzrY5eC2ue/Q2TOVtQ/7HhQfulW3IkwFUeoYKoz/11NiD7/eoS6l6rVLQ7INa/eJ95q6TN5VN7219JJIeqVNVrTj48OVgFLY36upNi9o72UzIad/Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780992736; c=relaxed/simple; bh=Ma8rDYc0g8Qe2kUIdmMo5fZVsxiokiehhNp2UHAZhiw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JgiUeR7+Azt98WPJ6dD6PR2cYC6SgJ4Ogv3zJ3niHJ2hh1/D1yi3NG8KkSoLFqDBJBjvY/EpTkY7vprrI+ztW3S98xuInmKciohrxqpzqOhEpPDwsvrmrYnEHv6fBSSbyOBTq1JmZhTXXEDEtpMBxo0XpBeabg3HJYQ8WxlOPTo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mBNfFi7p; 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="mBNfFi7p" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 414941F00893; Tue, 9 Jun 2026 08:12:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780992735; bh=6iy6WqC0AyHBkc7kR6hVPweXwlBpVwgmOI4XY3Av07c=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=mBNfFi7ppl4+IUjL4paapjKUUGOFLBiQiAJsdBQDha5aP4aWh/vLeYKkEYguX4EB8 ZBU3SBR96jhLjV1NqLg4LNvs+iSd0iB/5Y2Dd3MlHOIpLsMuIOehzo5Sn5rY7D12en A1bhQYr+0gvzV+z6xEZjwdZMka0w5T8ppl9kn1Rnoq2Dl/XprTERRJTJ+SImEIrg6Q CRLqd/6h4NBJOvnwoCC87TC0tOF6mamlktlGki3+Pt4XlKIrui0MLA+tnn4vUkhYQ7 XFbwRGDgXNzeKKthtrWKBPW4b+luJ0ChgndRKis1p9FUreefx9dSGBhJFmU/wEXuSG eAUkN7WiysX/A== Message-ID: Date: Tue, 9 Jun 2026 10:12:02 +0200 Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: New design To: Matthew Wilcox , "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, Jason Wang , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Muchun Song , Oscar Salvador , Andrew Morton , Lorenzo Stoakes , "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: 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 On 6/9/26 05:58, Matthew Wilcox wrote: > OK, here's how I'd structure this: > > 1. Introduce PG_zeroed for buddy pages > 2. Set it if init_on_free is set > 3. Set it from balloon driver > > https://lore.kernel.org/lkml/c7094de807c0e963526686e1d245bc76193b1a92.1776689093.git.mst@redhat.com/ > > but add FPI_ZEROED instead of an extra bool parameter. > > 4. Introduce page_is_zeroed like this: > > static inline bool page_is_zeroed(const struct page *page) > { > /* > * lru.next has bit 2 set if the page is already zeroed. > * Callers may simply overwrite it once they no longer > * need to preserve that information. > */ > return (unsigned long)page->lru.next & BIT(2); > } > > (you'll notice this is similar to page_is_pfmemalloc() but it doesn't > need to be in mm.h) > > This step is going to be a bit fiddly. We weren't expecting to return > multiple flags in page->lru.next, so clear_page_pfmemalloc() just sets > page->lru.next to NULL. So somewhere we need to make sure that > page->lru.next is definitely NULL, and then allow both the zeroed and > pfmemalloc flags to be set in it. > > The important part of this is that it allows the zeroed flag to be > returned from the page allocator without introducing pghint_t like you > did in v2. I previously raised (in v2? not sure) that we could using a pageflag that are only used for folios, and then simply clear that flag on the folio allocation path such that we don't get false-postives with the bit set. > > 5. Now you can start skipping various zeroing steps higher in the call > chain. > > I understand David's disgust with vma_alloc_zeroed_movable_folio() > but that is surely a separate cleanup and nothing to do with this > patchset. Well, in my reality, we're just finding interesting ways to work around the fact that GFP_ZERO sometimes does what we want, sometimes doesn't. So we leak information out of the buddy to really only handle one scenario: fixing up GFP_ZERO currently sometimes not doing what we want. I'm afraid we couldn't use the above trick to punch zeroed pages back into the buddy: some random user doing alloc+use+free would be unaware that there is a bit to clear. So I assume really only folio allocation would make use of this, to work around our problematic GFP_ZERO implementation. -- Cheers, David