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b=bw/JPR9uqN4l5Dxlb2N4tR3WTfviG/7xqecf/Jyr6pGYfeyUdqczyUH71g7LwG6Ib N4qV5KNb3VSbfVKOvCmvTaOAD0oGwPgmlJSDzrMeDJMuxCVoe9ALODHzXeNzDVs2IB 04m3EHp7gP16jBblhaVF2TafrDDLGu+shiq+7YWx0s+uDbEsyuwb36zIBqOWihC+AH M5bNkg81zo2yrAJoP68uAaUfpSPye9ZUoaGcEKujr4hrEdSwkV4tBWuiBcVu/9VGUc tfvLISkyYzaPHxrFKc8nT3WEtxqO+2DqxvxkQwYImDkT8Z/7drl2BVajvs0swnk3Cf EgSTQoM/Sbp/g== Message-ID: <94290ad5-f63d-4fa7-a898-dcfe6cd9998b@kernel.org> Date: Thu, 12 Mar 2026 22:00:23 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v15 06/13] mm/khugepaged: skip collapsing mTHP to smaller orders To: Nico Pache , 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, 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, 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 References: <20260226031741.230674-1-npache@redhat.com> <20260226032445.233437-1-npache@redhat.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: k9tesgnghgu8e3qt5e71a1iufmmo6wzk X-Rspamd-Server: rspam09 X-Rspam-User: X-Rspamd-Queue-Id: D651420002 X-HE-Tag: 1773349242-338273 X-HE-Meta: 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 /Dk6nwsK qtOgPaVL7hM/2PpYdZgCVm91oEGkPYoGj9NDPUMKpFW11W3wVPlX2gbxdCRLjDS/jgO9nM+AEHJeU4HREM7vcQc8F9QlJuav4G6BTgnvd6db/Nh9MYZToqnq65gozsmls5qyFQXpyxqyeU1H7HTLuyLh0vFDA3fjRuk4KHYj04Ymyt1uAo/cB9c6VFhawpFgcjhJr+p73Uh9Mrt4y5WG5y/vXKsNeQx5Tw8t7NeO1NxR15c34SOsujy2kK7nE4pgS8q/9fDRcnsCpGX2nTgTwRW4UMJxLpDHhNlCVnCHFSZJrrDlKX2KbLOUyRonVWSh4QPcDlqz6HcsquzMfpHdqMKDtk5KTpX8jQLVhyug7Yr8adY4/aFh6fihLQWpM9nfxEHFw3Md9floY4eP9KvnRE3x4si/wxHviyC93s7UzzgKdyqfk1Jk+1VcaJg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/26/26 04:24, Nico Pache wrote: > 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; Why aren't we doing the same in hpage_collapse_scan_pmd() ? -- Cheers, David