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Thu, 26 Feb 2026 03:24:57 +0000 (UTC) Received: from h1.redhat.com (unknown [10.22.64.173]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 9C8361955F43; Thu, 26 Feb 2026 03:24:47 +0000 (UTC) From: Nico Pache To: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Cc: aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, david@kernel.org, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, jackmanb@google.com, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, lance.yang@linux.dev, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, npache@redhat.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com Subject: [PATCH mm-unstable v15 06/13] mm/khugepaged: skip collapsing mTHP to smaller orders Date: Wed, 25 Feb 2026 20:24:45 -0700 Message-ID: <20260226032445.233437-1-npache@redhat.com> In-Reply-To: <20260226031741.230674-1-npache@redhat.com> References: <20260226031741.230674-1-npache@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: dZuxcqHE22g11RrNBOkKaHdO6AQ-T770gkjXFTa0PVQ_1772076297 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true X-Rspam-User: X-Rspamd-Queue-Id: 7FF0380008 X-Rspamd-Server: rspam02 X-Stat-Signature: sf16zuo8aaq1wjmq1tnc993fcfdp6kpn X-HE-Tag: 1772076305-890148 X-HE-Meta: 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 3kMGdEdp 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 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 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 fb3ba8fe5a6c..c739f26dd61e 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -638,6 +638,14 @@ 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; -- 2.53.0