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[2003:d8:2f1d:ed00:1769:dd7c:7208:eb33]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8e0d758sm17727799f8f.49.2025.07.16.07.32.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Jul 2025 07:32:44 -0700 (PDT) Message-ID: <290d669f-e358-471a-95b7-c46f974742d0@redhat.com> Date: Wed, 16 Jul 2025 16:32:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 08/14] khugepaged: skip collapsing mTHP to smaller orders To: Nico Pache , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: 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, kirill.shutemov@linux.intel.com, 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 References: <20250714003207.113275-1-npache@redhat.com> <20250714003207.113275-9-npache@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 001F040017 X-Rspam-User: X-Rspamd-Server: rspam09 X-Stat-Signature: g5yi46hdznd46jaapqabhgh4tkkusjc3 X-HE-Tag: 1752676369-488753 X-HE-Meta: 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 3vucO35u 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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: On 14.07.25 02:32, 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: Baolin Wang > Co-developed-by: Dev Jain > Signed-off-by: Dev Jain > Signed-off-by: Nico Pache > --- > mm/khugepaged.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 5d7c5be9097e..a701d9f0f158 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -612,7 +612,12 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > folio = page_folio(page); > VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio); > > - /* See hpage_collapse_scan_pmd(). */ > + if (order != HPAGE_PMD_ORDER && folio_order(folio) >= order) { > + result = SCAN_PTE_MAPPED_HUGEPAGE; > + goto out; > + } Probably worth adding a TODO in the code like /* * TODO: In some cases of partially-mapped folios, we'd actually * want to collapse. */ Acked-by: David Hildenbrand -- Cheers, David / dhildenb