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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780901976; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Y3/06Trq5FpnxHyx8TwAa3S5P3cfEJjPOzAapv5j8wo=; b=EUapOzUXzSldul+SfubS/o+1vi1bdkmgOGo33ORWMjo36vmrsTNcL+aaGW03/YjqAZSW2R k6K4Jlx7h9j38VtG8xzTPjXnNZRTsV7JRAyL8HPHWR9Zi+NmmnQyClmfyWfUeVsdt9mjuP MnaxxTrabdkE3hKr88UNKrlypvcKGKk= From: Lance Yang To: npache@redhat.com Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, 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@infradead.org, ljs@kernel.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.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, usama.arif@linux.dev Subject: Re: [PATCH mm-unstable v19 07/14] mm/khugepaged: skip collapsing mTHP to smaller orders Date: Mon, 8 Jun 2026 14:59:06 +0800 Message-Id: <20260608065906.66125-1-lance.yang@linux.dev> In-Reply-To: <20260605161422.213817-8-npache@redhat.com> References: <20260605161422.213817-8-npache@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 47F2B14000F X-Stat-Signature: k68ut5thzzrb5ftzbxtbqq4jwgjnw1f1 X-HE-Tag: 1780901982-667139 X-HE-Meta: U2FsdGVkX18NwVZalr8OHqS+QQF7wIZCJ/WnDcpHDJOsPNyP5HlSNdjIB4xZq1Z8L1Y8iNflgxQ2fKwWoaWuD+GHkDGQ+VYtUkBDGs2mnlk+keBvV+JophYap3xhH4TFdLQi8jSWJJqfIChOdGoAHbBhhZIkQvLkLSIAXrem0zAS+I2oGQuh52vqZQ3VTarfZ++leRK2311sYz5g0Ivo4+hFTwWmWQvjGrnJ33/xvBLEFaJjLwU2sp5/3WiGUpyYd+RnpBt6CLf5CdmZvmQxf02cZFxkfrWvRIS11Akexh0ri6RzzegWC7untQfrrPU3R6iBjopAWgsFMWOMbWRO5v4eiZt98UrP/znhZd29Mxy0ZUooBbN4EfZAA8Bc6lDLiowCuSovTCdq2NMTkrpHcKgBB2qqGUhmv/Y/5MN8vuynZOayRQIzerSArwUS6qd3HZjNtXV6D7GW86Yh40O/uFFFNG9i9x27lx0y/t1sGSzUotJdo9ZPfzzleA8BojjR+BDDnawz3VAJZj+TxDGI3usMFXww5g7hqJlK9873XtakQ57ZviXs06PtORVlLDMjmu6sGeqTa5xQylAO8Bl+yjVhUGmcwUDwaz/ql5Aoe4HhFa8ijDEDuzbVW0uIXu25HuVqUUa2SXqUwniIYQJVY/cRF/leXHSKQuZRcO1S6P5HTFGYoF1Av9fgAEMROnaPs3Y7K/66CKGBDBMEwuQHJ5QZbzowBBCpiS4BoA4y1T9nDCdNHIz8FCh1CSuqA98vTnkzuTKIYYzFAhMdYEEUrU736FsScxoaC3SpDJ89xm7TO5xzcAWBd7J2WzWS15QfXNQRvKkX0qQI/PmVb3e0i2YduBNFvF6MREGxGNRznxXvmhouGCj/6i5IvGbAGqRZdj1F69bIcXNJLgIH1/jQgYQODf2Qbl1WGjmSkWQK/jHQqYmWOsPY5/YmXn5rUOZr8T1UOKvyniHyO7GuLoh C6vOSioo 55BJdOUD2iM6EqV6x65F0wsdybjuArlN/Mr2Lj1wSw09cQjdXTx+iV5jN9u72pjErbDZzI4SHTE5xWH81yiHuDuWbTCs7aBnhjLqvQq+vhIbSS43FqLzCn8xTKNUKIMDLizq0IlJ4h0hOcJXK3Y1t4IGx7OhpkCjGM1OBX4Dh3mzQF3rmduIUmw/nBqhEA5EviBBsbyXJ9/hmfKhhm18qjHp8+PBCVOy0PBbJxiyqiljO0pRL4ptREExPcsDPGjKJI5SmwbI8vYYGhfGopTva3Rwb3fvxi2+OKEnbUHYKDeOOmT52EHclkjSJ8HRxMT7/N+OTIbAv6kpjMqtobDm3r3RMLL5EVG1xOM9HIv6VerNctARxgbKILFdf5LuppfHgylpjUYJ14LO8f64pLGYHN6LTQyr2IJuOLMNK Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jun 05, 2026 at 10:14:14AM -0600, Nico Pache wrote: >khugepaged may try to collapse a mTHP to a folio of equal or smaller size, >possibly resulting in a partially mapped source folio, which is undesired. >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 >check is not done during the scan phase as the current collapse order is >unknown at that time. > >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 (arm) >Acked-by: Usama Arif >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 c2769d82a719..191e529c185c 100644 >--- a/mm/khugepaged.c >+++ b/mm/khugepaged.c >@@ -697,6 +697,14 @@ 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. >+ */ Partially mapped folios can be handled later :) Reviewed-by: Lance Yang >+ if (!is_pmd_order(order) && folio_order(folio) >= order) { >+ result = SCAN_PTE_MAPPED_HUGEPAGE; >+ goto out; >+ } > > if (folio_test_large(folio)) { > struct folio *f; >-- >2.54.0 > >