From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 755DD33FE26; Mon, 13 Apr 2026 19:12:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776107520; cv=none; b=KHBNBGTUD1Blm3mwBmeXZVuG4IgukSEBVPNemLtAZaTUjmSJ+stX05uKo2EidBOgrmXOtoAg2d6UC1b20gsHqDZgEslpRvaQJx7Nzn6JjJAgIgmeIGYTuCDxXhQzCReDVjd9Yw2CCVRbLGj3DWz56v+NiQ+n3DCzcSMiVZc7CnQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776107520; c=relaxed/simple; bh=MxX8wt+PtDGl8J/2Seud1f/icOdBa7LsiBhLxw5jILY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=A9WSWUdsgBekdjI1EvnVRc7OvFDMFhSGlpiA0oFHgkcNDhZFM8ZFT6iGas5PATWxv+0VWerfRLiQHgdraVG/HDLzBoX3OtaYvwQyQLFUP6d+dadvm0REr8sebpHMUGrg040XJdIwTC1qjM4M1rflxcjRRESFH7Gi1F8YFshxSb0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lN2KnZxk; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="lN2KnZxk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EE510C2BCAF; Mon, 13 Apr 2026 19:11:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776107520; bh=MxX8wt+PtDGl8J/2Seud1f/icOdBa7LsiBhLxw5jILY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=lN2KnZxkDamOr6ulzzzsOtuWkA9vGRCPVx1F7hCKAlborqdv6Y7xznBREeJUgcwif LfCfPa0d2oFzzrcr5dwMggI6fAmOxdMUL/B21wWunAD9fBqJJpu3xw4uGyvbfBfkxo T+EoaympWixmlhFmF6R8v+zQfFavbTfsTcqf4SMRSsp82C7P9aL5tQSygcgP6gMg9f 2DuMDBo7RVVBNlzMnOr0u9YOieF5MWFWZxw5aBrttOe9dyY/pqfq3rSWn1df/I6eiC zNWbe4m5zoZSZ0afgU3Emk1FffKHWsjQosY7C8iczzqPr2cHKw6ygl0MSNTapi6gFM +m+h/e9LvGQ5w== Message-ID: Date: Mon, 13 Apr 2026 21:11:51 +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: [PATCH RFC 1/9] mm: page_alloc: propagate PageReported flag across buddy splits To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org Cc: Andrew Morton , Vlastimil Babka , Brendan Jackman , Michal Hocko , Suren Baghdasaryan , Jason Wang , Andrea Arcangeli , linux-mm@kvack.org, virtualization@lists.linux.dev, Johannes Weiner , Zi Yan 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 4/13/26 00:50, Michael S. Tsirkin wrote: > When a reported free page is split via expand() to satisfy a > smaller allocation, the sub-pages placed back on the free lists > lose the PageReported flag. This means they will be unnecessarily > re-reported to the hypervisor in the next reporting cycle, wasting > work. > > Propagate the PageReported flag to sub-pages during expand() so > that they are recognized as already-reported. > > Signed-off-by: Michael S. Tsirkin > Assisted-by: Claude:claude-opus-4-6 > --- > mm/page_alloc.c | 17 ++++++++++++++--- > 1 file changed, 14 insertions(+), 3 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 2d4b6f1a554e..edbb1edf463d 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1730,7 +1730,7 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn, > * -- nyc > */ > static inline unsigned int expand(struct zone *zone, struct page *page, int low, > - int high, int migratetype) > + int high, int migratetype, bool reported) > { > unsigned int size = 1 << high; > unsigned int nr_added = 0; > @@ -1752,6 +1752,15 @@ static inline unsigned int expand(struct zone *zone, struct page *page, int low, > __add_to_free_list(&page[size], zone, high, migratetype, false); > set_buddy_order(&page[size], high); > nr_added += size; > + > + /* > + * The parent page has been reported to the host. The > + * sub-pages are part of the same reported block, so mark > + * them reported too. This avoids re-reporting pages that > + * the host already knows about. > + */ The comment is a bit excessive. I'd say you can drop it completely. > + if (reported) > + __SetPageReported(&page[size]); > } > > return nr_added; > @@ -1762,9 +1771,10 @@ static __always_inline void page_del_and_expand(struct zone *zone, > int high, int migratetype) > { > int nr_pages = 1 << high; > + bool was_reported = page_reported(page); > > __del_page_from_free_list(page, zone, high, migratetype); > - nr_pages -= expand(zone, page, low, high, migratetype); > + nr_pages -= expand(zone, page, low, high, migratetype, was_reported); > account_freepages(zone, -nr_pages, migratetype); > } > > @@ -2322,7 +2332,8 @@ try_to_claim_block(struct zone *zone, struct page *page, > > del_page_from_free_list(page, zone, current_order, block_type); > change_pageblock_range(page, current_order, start_type); > - nr_added = expand(zone, page, order, current_order, start_type); > + nr_added = expand(zone, page, order, current_order, start_type, > + false); In MM land we started doing /* reported= */false This raises a good question: how does buddy merging handle the reported flag? -- Cheers, David