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Mon, 1 Dec 2025 17:48:54 +0000 (UTC) Received: from h1.redhat.com (unknown [10.22.66.60]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 9FBB81800451; Mon, 1 Dec 2025 17:48:45 +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 v13 mm-new 09/16] khugepaged: skip collapsing mTHP to smaller orders Date: Mon, 1 Dec 2025 10:46:20 -0700 Message-ID: <20251201174627.23295-10-npache@redhat.com> In-Reply-To: <20251201174627.23295-1-npache@redhat.com> References: <20251201174627.23295-1-npache@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 4709EC0016 X-Stat-Signature: n15n44hat94ox3j8dygjpaca1mub995d X-Rspam-User: X-HE-Tag: 1764611345-975973 X-HE-Meta: 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 0NmuhqLP 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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 b41f68bbac80..b2ea56c9bb42 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -641,6 +641,14 @@ 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 (is_mthp_order(order) && folio_order(folio) >= order) { + result = SCAN_PTE_MAPPED_HUGEPAGE; + goto out; + } if (folio_test_large(folio)) { struct folio *f; -- 2.51.1