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Thu, 22 Jan 2026 19:31:31 +0000 (UTC) Received: from h1.redhat.com (unknown [10.22.88.59]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 9B7D71958DC2; Thu, 22 Jan 2026 19:31:22 +0000 (UTC) From: Nico Pache To: linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: npache@redhat.com, akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, corbet@lwn.net, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, jannh@google.com, pfalcato@suse.de, jackmanb@google.com, hannes@cmpxchg.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, zokeefe@google.com, rientjes@google.com, rdunlap@infradead.org, hughd@google.com, richard.weiyang@gmail.com, David Hildenbrand Subject: [PATCH mm-unstable v14 09/16] khugepaged: skip collapsing mTHP to smaller orders Date: Thu, 22 Jan 2026 12:28:34 -0700 Message-ID: <20260122192841.128719-10-npache@redhat.com> In-Reply-To: <20260122192841.128719-1-npache@redhat.com> References: <20260122192841.128719-1-npache@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: ahyvXJ4le3Gh9FiIPSC7mQ96jm9_8V1q4yutbLt94f4_1769110292 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true X-Rspamd-Server: rspam12 X-Stat-Signature: mkuan4s1731rfd736yeid94ttrktex15 X-Rspamd-Queue-Id: A35BE18000D X-Rspam-User: X-HE-Tag: 1769110302-418683 X-HE-Meta: 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 3X1qyaYA 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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 76cb17243793..8bb70e1401ad 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -639,6 +639,14 @@ static enum scan_result __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 (!is_pmd_order(order) && folio_order(folio) >= order) { + result = SCAN_PTE_MAPPED_HUGEPAGE; + goto out; + } if (folio_test_large(folio)) { struct folio *f; -- 2.52.0