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b=FTqAzh0eoHtfHa84KS84sbt9TpcXbmAjmqfiJGfnp8JSxiXMWmIjweIjT82sFchl7JFjJO0QPldWqRMRUX9Lug2Df+RATTHLCCxcFsR4yEYHbWGCc1hBHePYhetO6UD8+a0i7HJnacQAZvgigrmX8PlOHamg8snrNGhH8t9Ib7Eiez0y8LnFIMes3bfB++x7f1bIl0fbaxYYi3Y9hCrRpc1C7g1XiYNRUQHh6ieBP+oPp6+l8eV9y2blLq0iVubxd2kBRQyayUGLZkLrunMPr5lg5ho6kTH/UNlo0EBTxtLvH+boeiB/X6t3uYbdHyXIlBo5sIv4ks0lD396sbMKAQ== Received: from IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) by DM4PR12MB7765.namprd12.prod.outlook.com (2603:10b6:8:113::5) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.496.23; Fri, 16 Oct 2026 02:47:10 +0000 Received: from IA0PR12MB8374.namprd12.prod.outlook.com ([fe80::d85f:4c87:ae84:3f16]) by IA0PR12MB8374.namprd12.prod.outlook.com ([fe80::d85f:4c87:ae84:3f16%6]) with mapi id 15.21.0472.016; Fri, 16 Oct 2026 02:47:10 +0000 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Thu, 15 Oct 2026 22:47:09 -0400 Message-Id: From: "Zi Yan" Subject: Re: [PATCH for 7.4-rc2+ 7/7] mm/rmap: re-enable discarding lazyfree THPs at PMD level Cc: , , "Zi Yan" To: "David Hildenbrand" , "Baolin Wang" , "Liam R. Howlett" , "Nico Pache" , "Ryan Roberts" , "Dev Jain" , "Barry Song" , "Lance Yang" , "Usama Arif" , "Kiryl Shutsemau" , "Lorenzo Stoakes" , "Rik van Riel" , "Vlastimil Babka" , "Harry Yoo" , "Jann Horn" , "Kyle Zeng" , "Andrew Morton" X-Mailer: aerc 0.22.0 References: <20261015-anon_vma_uaf_fix-v1-0-7b977303b42b@nvidia.com> <20261015-anon_vma_uaf_fix-v1-7-7b977303b42b@nvidia.com> In-Reply-To: <20261015-anon_vma_uaf_fix-v1-7-7b977303b42b@nvidia.com> X-ClientProxiedBy: MN0PR02CA0006.namprd02.prod.outlook.com (2603:10b6:208:530::24) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|DM4PR12MB7765:EE_ X-MS-Office365-Filtering-Correlation-Id: 2d5fd1cd-4167-478d-0af9-08df2b2fc698 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: 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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 Thu Oct 15, 2026 at 2:13 PM EDT, Zi Yan wrote: > The patch "mm/rmap: don't discard lazyfree THPs at PMD level" disabled > the PMD-level discard, because it cleared the PMD before checking whether > the folio could be discarded, and munmap() or mremap() could skip that > transiently none PMD. > > __discard_anon_folio_pmd_locked() now keeps the PMD invalidated, not > cleared, until the discard is committed, GUP-fast no longer follows an > invalidated PMD on any architecture, powerpc page table check no longer > counts an invalidated PMD as mapped, and sparc64 keeps thp_pte_count > balanced when an invalidated PMD is set again or cleared. Discard lazyfre= e > THPs at PMD level again. > > Assisted-by: LLM > Signed-off-by: Zi Yan > To: Andrew Morton > To: David Hildenbrand > To: Lorenzo Stoakes > Cc: Rik van Riel > Cc: "Liam R. Howlett" > Cc: Vlastimil Babka > Cc: Harry Yoo > Cc: Jann Horn > Cc: Lance Yang > Cc: Kyle Zeng > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > --- > mm/rmap.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/mm/rmap.c b/mm/rmap.c > index 1131b76bbbc28..805db93fe0428 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -2275,6 +2275,17 @@ static bool try_to_unmap_one(struct folio *folio, = struct vm_area_struct *vma, > } > =20 > if (!pvmw.pte) { > + if (folio_test_lazyfree(folio)) { > + if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, folio)) Sashiko mentioned that unmap_huge_pmd_locked() does add_mm_counter() without calling update_hiwater_rss() first so that peak RSS can be under-reported. Answer: yes, I fixed it locally by calling update_hiwater_rss() before unmap_huge_pmd_locked(). > + goto walk_done; > + /* > + * unmap_huge_pmd_locked has either already marked > + * the folio as swap-backed or decided to retain it > + * due to GUP or speculative references. > + */ > + goto walk_abort; > + } > + > if (flags & TTU_SPLIT_HUGE_PMD) { > /* > * We temporarily have to drop the PTL and --=20 Best Regards, Yan, Zi