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 43D973A4505 for ; Wed, 1 Jul 2026 08:56:53 +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=1782896215; cv=none; b=MAQ9URzVpaMTknz/r+1TLJWsvg7aT6cCQvlPjfT4ihjhYjOPcN+j4Vj1ydczDTmWEwgJpK4ji4ebqLKYZQy5d+lFF1y/8cfPNZwajb85Mb1hNlbWk+kMmVlgtFvuFqUlekvEv5mXFG7THIOwbobHE04n39Tkmjc/WprcqpGoDBI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782896215; c=relaxed/simple; bh=4/VVJS4QcUQpYrw71aJole9czGrzQThVZJHZ66bA01s=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YGKUZHfvjWVaBlYq3pPHcZYPnUTsSPRfLQYJ5qAWL6cAhaZP23qQKEn4+BDiy5COo8CuBCu1pmrFptldE7qOzZsIahmRCv1IjkHVa5yRuIiYVssDP+CHOEfNN5sBs81uJIv8jqfbEMJaOdoQz8KcZymcielgIDj3GR+bcCngQI8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oNMRHBeL; 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="oNMRHBeL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 20E691F000E9; Wed, 1 Jul 2026 08:56:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782896213; bh=IZ50nr0AcHZh8ITCWlGZKEWtSEWm6cGO1t20uNGyx4c=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=oNMRHBeLVJEjyBCVIOyZwbJuJWjy4aclyojSaJbTZm7x6ljvpBHyBpsGnAQPrlm5d 9pv3guPknWP21IPaX5BiKCFroDCPZaYod3KyhpuyvMIr4gXeZw+0pohRPo7w5I1m7B M8lH89y6HA4nggcJ5T7ptiCHTGJEDhj70Wxd4MgKqyC1p7zRcjcy26bi+/MiHxb5cC xEuOKP7Y3WE5BWJ3XhumRd0wkm+l3zqs6IYhaqbhVqsOzaLcdcYpKmHQM1NBdgs6cf uI43joE12KhYi5z8onraPLG2JHQfF/UHtTpPhOgahZuzCLK9gSspytjDG2DTdgyurH OCoDp4F5SBg8g== Message-ID: <98cf3340-1a2f-4d50-8410-6e9d6d3a5308@kernel.org> Date: Wed, 1 Jul 2026 10:56:47 +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 2/4] mm/huge_memory: add page->private check back in __split_folio_to_order() To: "Vlastimil Babka (SUSE)" , Zi Yan , Andrew Morton , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Mike Rapoport Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260628-keep-subpage-private-zero-at-free-v1-0-f4ce3930d10f@nvidia.com> <20260628-keep-subpage-private-zero-at-free-v1-2-f4ce3930d10f@nvidia.com> <9fe5173c-4beb-42fe-8f7e-385c609f899f@kernel.org> 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: <9fe5173c-4beb-42fe-8f7e-385c609f899f@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/29/26 16:39, Vlastimil Babka (SUSE) wrote: > On 6/29/26 04:56, Zi Yan wrote: s/add/readd/ >> page->private should not be set in tail pages. Commit 4265d67e405a >> ("mm/migrate_device: add THP splitting during migration") removed it >> without a proper reason. Add it back. You can link to the discussion where we clarified that this was not intentional. >> >> Signed-off-by: Zi Yan >> --- >> mm/huge_memory.c | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 2bccb0a53a0a..037d67fbec6e 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -3594,6 +3594,16 @@ static void __split_folio_to_order(struct folio *folio, int old_order, >> new_folio->mapping = folio->mapping; >> new_folio->index = folio->index + i; >> >> + /* >> + * page->private should not be set in tail pages. Fix up and warn once >> + * if private is unexpectedly set. Do it before swap.val assignment >> + * since private overlaps with swap.val. >> + */ >> + if (unlikely(new_folio->private)) { >> + VM_WARN_ON_ONCE_PAGE(true, new_head); >> + new_folio->private = NULL; >> + } > > The unconditional warning means this is not expected to happen. In that case > it's odd to check and fixup always, but only warn with CONFIG_DEBUG_VM. > > If we are reasonably sure the current code is OK, and only want to catch new > mistakes in development, we could just VM_WARN_ON_ONCE_PAGE() without fixup. > > If we are paranoid, leave it as it is, but drop the "VM_" ? Agreed, either "if (WARN_ON_ONCE(new_folio->private))" + fixup, or no fixup. I'd prefer VM_WARN_ON_ONCE_PAGE(). (I was only able to trigger this once while testing my own patches) -- Cheers, David