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 DA241C44532 for ; Tue, 21 Jul 2026 14:34:06 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9EC2A6B00BD; Tue, 21 Jul 2026 10:34:05 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 99CF66B00BF; Tue, 21 Jul 2026 10:34:05 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 88D1B6B00C1; Tue, 21 Jul 2026 10:34:05 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 4DC326B00BD for ; Tue, 21 Jul 2026 10:34:05 -0400 (EDT) Received: from smtpin18.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay10.hostedemail.com (Postfix) with ESMTP id CA092C01C2 for ; Tue, 21 Jul 2026 14:34:04 +0000 (UTC) X-FDA: 85013028408.18.9824B5A Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf02.hostedemail.com (Postfix) with ESMTP id 112D280012 for ; Tue, 21 Jul 2026 14:34:02 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="Wxp/mt8s"; spf=pass (imf02.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=1784644443; 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=+5YEfpnT2oozYCnmAI9PBP18Duhq3Tk/K6j/fOF23yk=; b=O/Z/e+rrEde2HdCvLmmiwOsieSXqZxG/82pMuS2sHGRSutXWraU1XeWM/kGf283OQ2E0xa mT8rfG6fuBlbeqTJG7ceJ5ZTgvOyu9+jO4RkJD6MNBheU7E5i+nxJfn2IqzuJi/lBuIlA3 l8ARfdyP5iBpQtHqOoCF8wUntEqfB90= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="Wxp/mt8s"; spf=pass (imf02.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=1784644443; b=CGi2LtBBKVh0Gkes/UccGu282eIuwwFfVz2U0b7gJ0XODScboqAzwz48aKZmy5UEGlJrJM 2RyfKMlJqve0lu/LDZOuRzFk4OYW+qIXyvVL11LqLg/mxsQH9tCeSzAMYB4ueVtXWWjoCY XpO4l5SucDTbaAlGxNJ5q6mrD8Fb3GQ= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 7074C60054; Tue, 21 Jul 2026 14:34:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EDE2C1F00A3A; Tue, 21 Jul 2026 14:33:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784644442; bh=+5YEfpnT2oozYCnmAI9PBP18Duhq3Tk/K6j/fOF23yk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Wxp/mt8stG+Rc3giQdEBOVq+M0GGJSxpatj/AoGDI11QtjXS++ZO3wst/OIYM3b+r p9xtA5OgnMxY8dIyiwhcIvrkRVCBOBQ8YBmY3DksE6a0d5zJRIS/HAauMMyXw6oMkq +sz2KJK77Rzf5Jt9gxktu0YKZM2amQS9iECJzzhW5wNRrGP+vdSAecoik8quLZwLqt vak91HwBcii9zp7Z7lkEDw8ech5OBrEC04OC185A/7SqwhOB9iWLfQRuc2beb2oLrP G4O0vSF/2WUqDAhnU9fglU6QjsrTq+g32MQsBhN7FxEY9PFtiwPp69FWML+JwW/TSS GKjDoyaD/YOZA== Message-ID: <5766bfae-8dd9-4542-bbab-324dbde0e2f5@kernel.org> Date: Tue, 21 Jul 2026 16:33:56 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/2] mm: fix PMD level mTHP accounting bugs To: Nico Pache , Andrew Morton , Jason Gunthorpe , "Lorenzo Stoakes (Oracle)" , Alistair Popple , Oscar Salvador Cc: Barry Song , linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, willy@infradead.org, Zi Yan , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang References: <20260717064502.1980173-1-npache@redhat.com> <20260717182947.534af296aaa1831d13f8ae6d@linux-foundation.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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 112D280012 X-Rspamd-Server: rspam01 X-Stat-Signature: 697ni1jpjcjmdrpsnfs6ro74o4rbq9jg X-HE-Tag: 1784644442-429658 X-HE-Meta: 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 Rv7zJJlP 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/21/26 15:57, Nico Pache wrote: > On Fri, Jul 17, 2026 at 7:29 PM Andrew Morton wrote: >> >> On Fri, 17 Jul 2026 00:44:58 -0600 Nico Pache wrote: >> >>> While running selftests I noticed the PMD level per-mTHP stats (nr_anon) >>> remained elevated after each run. After further investigation I noticed >>> this accounting error occurs for both the migration.private_anon_htlb_test >>> and the HMM tests. >>> >>> In the HMM case this is due to folio_add_new_anon_rmap() incrementing the >>> mTHP stats, but never containing a corresponding decrement in >>> free_zone_device_folio(). We solve this by making sure to decrement the >>> counter when freeing device memory. >>> >>> In the migration case, we are incrementing this counter without first >>> checking whether this folio is a hugetlb folio, which relies on a separate >>> accounting system. We solve this by adding the proper hugetlb check before >>> incrementing this counter. >>> >>> With these changes in place, the two tests no longer cause elevated PMD >>> level accounting issues. >> >> Thanks, I've updated mm.git's mm-hotfixes-unstable branch to this >> version. > > Thanks! > >> >> Sashiko is worried about the existing code ("list corruption or a >> use-after-free panic"): >> https://sashiko.dev/#/patchset/20260717064502.1980173-1-npache@redhat.com > > https://sashiko.dev/#/patchset/20260717064502.1980173-1-npache@redhat.com > > I dug into this, although I'm not very familiar with device memory. In general: Don't let a tool waste your time on unrelated things if it wasn't you that asked the tool for it. Someone else asked the tool to find unrelated things. I thought we only support anonymous THP for device-private, not device-coherent. Maybe lib/test_hmm.c could somehow trigger it by selecting MIGRATE_VMA_SELECT_COMPOUND? But in migrate_device_coherent_folio() we have WARN_ON_ONCE(folio_test_large(folio)); So this would already be pretty broken and I wouldn't spend any more time on it. -- Cheers, David