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Wed, 22 Oct 2025 18:39:42 +0000 (UTC) Received: from h1.redhat.com (unknown [10.22.64.41]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id AE46119560B6; Wed, 22 Oct 2025 18:39:29 +0000 (UTC) From: Nico Pache To: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org Cc: david@redhat.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, dev.jain@arm.com, corbet@lwn.net, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, akpm@linux-foundation.org, baohua@kernel.org, willy@infradead.org, peterx@redhat.com, wangkefeng.wang@huawei.com, usamaarif642@gmail.com, sunnanyong@huawei.com, vishal.moola@gmail.com, thomas.hellstrom@linux.intel.com, yang@os.amperecomputing.com, kas@kernel.org, aarcange@redhat.com, raquini@redhat.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, tiwai@suse.de, will@kernel.org, dave.hansen@linux.intel.com, jack@suse.cz, cl@gentwo.org, jglisse@google.com, surenb@google.com, zokeefe@google.com, hannes@cmpxchg.org, rientjes@google.com, mhocko@suse.com, rdunlap@infradead.org, hughd@google.com, richard.weiyang@gmail.com, lance.yang@linux.dev, vbabka@suse.cz, rppt@kernel.org, jannh@google.com, pfalcato@suse.de Subject: [PATCH v12 mm-new 08/15] khugepaged: skip collapsing mTHP to smaller orders Date: Wed, 22 Oct 2025 12:37:10 -0600 Message-ID: <20251022183717.70829-9-npache@redhat.com> In-Reply-To: <20251022183717.70829-1-npache@redhat.com> References: <20251022183717.70829-1-npache@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 4D0A5120002 X-Stat-Signature: yaxjktbpjezisskxqs55645n9cyhn6g4 X-HE-Tag: 1761158391-332364 X-HE-Meta: U2FsdGVkX186w38E2n/LwZ+0ghUgzVoOESocnNmsJcfrrH1yhqhvPo3RxnL/H4voMottncf5yDIJwjVyHJqyfzt5nfgfSjFzpwEXvO4EOoUJrEOu4fRYBNNg/lwx5aHrSQcdb5JqmhEMr71VKFqoJYwFZijmlELGJ1SQtYOaEKNQwdVleErEaqKbd7PCleZaWvpzmeEHh+PYv4yhXGGNrkWYuvGANEHwr1v/8REU/giTimO4aZ4/yLpkfu51boegyODBICLXOWzVI0Z3t/3+xrofVKFIu1IT7rB2Xj9+X+ZzU/SwwJV6zoj0sewQXEQDc58ybfndoLGf+i+8d0kirqL7NzAnE7sBuopxIUWd92SqZSRI1DY1VQJTLpVj/jKgobPJpjuSMm5kSBBXTX5Z2sCJnhcC5t+Qgu3ilJRI8nMko898joWwPL9Dz8Sy7K0rpfU4VKVDiQBQx+aTkXPK+6K6vB3ndadUsR4XQ/FrVbef00deA7lfxJ/DbNufzTs0FAknxluG4ONNswadK2napX+QezpIYXq28PglRp7urRnlDRK6PHmnbI7oWLH+Wr3T8WkK2TBdOlWrgy1MAK5HEF8R0r6KpYHOG2ruSY80rBeE6MhYiBkO/d2etg3Htt6U0XiI2uDOzErRkWdNqabHvVNbzAJYo8gg7hocdl7bHCd5vuSUIsVs8SAGMO+RK0kO220Tapz8z4J9/C3447sBjqephFpIPSid2c90JaJMEb81JI1KehzR5/SkdtN51aiF60egoJgYu7y2VzISTAFSSEX2t/zOAyrpv81AD+mYp7zJhye5wfch19pjMN8TH6EYZqpZqfAJPdNskpGggUzDnmNLsTefX03BzY1NlBVIJoPOd5HaV299wZa4O0M91E4Kp67j4DU8OayEIa1hme4qV3oPRiJiMfn5Twg4bGf7VdkTnF242vZyScCieXM2q5XocRigURAlTuJ2r7ckGYf wAzYuKKX 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: khugepaged may try to collapse a mTHP to a smaller mTHP, resulting in some pages being unmapped. Skip these cases until we have a way to check if its ok to collapse to a smaller mTHP size (like in the case of a partially mapped folio). This patch is inspired by Dev Jain's work on khugepaged mTHP support [1]. [1] https://lore.kernel.org/lkml/20241216165105.56185-11-dev.jain@arm.com/ Reviewed-by: Lorenzo Stoakes Reviewed-by: Baolin Wang Acked-by: David Hildenbrand Co-developed-by: Dev Jain Signed-off-by: Dev Jain Signed-off-by: Nico Pache --- mm/khugepaged.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 75e7ebdccc36..d741af15e18c 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -629,6 +629,14 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, goto out; } } + /* + * TODO: In some cases of partially-mapped folios, we'd actually + * want to collapse. + */ + if (order != HPAGE_PMD_ORDER && folio_order(folio) >= order) { + result = SCAN_PTE_MAPPED_HUGEPAGE; + goto out; + } if (folio_test_large(folio)) { struct folio *f; -- 2.51.0