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 72FC7C43458 for ; Wed, 1 Jul 2026 08:56:58 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 5F4C36B00AC; Wed, 1 Jul 2026 04:56:57 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5CC0F6B00B0; Wed, 1 Jul 2026 04:56:57 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4BC306B00B1; Wed, 1 Jul 2026 04:56:57 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 13F316B00AC for ; Wed, 1 Jul 2026 04:56:57 -0400 (EDT) Received: from smtpin06.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 875421C19FC for ; Wed, 1 Jul 2026 08:56:56 +0000 (UTC) X-FDA: 84939602832.06.B190DB3 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf01.hostedemail.com (Postfix) with ESMTP id C51CC40003 for ; Wed, 1 Jul 2026 08:56:54 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=oNMRHBeL; spf=pass (imf01.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=1782896214; b=4iimX7880i2cqKOs9DhmLENshs0CMKAD0D664d3elcnyTOfR8zhLpx983SE1dj02PlapAp yuhH4xSNHLCm393xsQUAu0LW4ZVTaWDqRr1G/dv9O9Zq5VIpbtNN9sTuaEQAWmGY6UmAhA wLBW5eRnyZfnRd7Xk+RyJ6DU9F6g1xY= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1782896214; 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=IZ50nr0AcHZh8ITCWlGZKEWtSEWm6cGO1t20uNGyx4c=; b=sr7xpuzMAS2ac91rE0kORyeKFfea1/u1j6EjvzILPWdF67cElPBcoCvsFzGjrkOJEZ6cr2 bFBCd3razwnzoPeMSPwCYPIGHDs3q9yu5d7rhgjBXYyULlpQxRLD1y/6q+d62pBMJKlkwn zvsYHhBbuvpzxu1nx87G7FB74IN+SZ0= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=oNMRHBeL; spf=pass (imf01.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 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 2677C600AB; Wed, 1 Jul 2026 08:56:54 +0000 (UTC) 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 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 X-Rspam-User: X-Stat-Signature: 4ar314g9fruff5eeq7dgmzgobxk7o8jc X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: C51CC40003 X-HE-Tag: 1782896214-168155 X-HE-Meta: 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 2NDyo4Pz ImZ5BYA1FXPmssllA5q0ExsAW/XuKGhXlSTRJUF7YfYpt2UxUBrzEw+3FSW2a25ABBr9mnlGWjhoAZOsQZJcQA8x/RTIX5i9leOSCi/pmp+I57s0gBgNLLlQWrraTY1qe725qaaaMPXxC/wHCR8SpfvixqmJhx63qbGZru5i3Vnyd5nH6HQXRfcdhjBGoU3lKXFzVl39cK+y+LqSQcMewF7IjwZz1otie0g0IJGkayGAnnvwgHQgJI5wj7gGjdGuI9tGHwXJBrOxoSj5rp+SDcdbUduZe3mleskdP1T6wgzEnWciFvIQEcv0dqhyYwbYl+WmN10d/1mguj0A= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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