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Tsirkin" , Michal Hocko , Muchun Song , "Aneesh Kumar K.V" , Tejun Heo References: <563d1eef-b780-835a-ebf0-88ae111b20c2@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63W5Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAjwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat GmbH Message-ID: <65a1946f-dbf9-5767-5b51-9c1b786051d1@redhat.com> Date: Wed, 14 Oct 2020 20:18:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Content-Transfer-Encoding: quoted-printable 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: On 14.10.20 19:56, Mina Almasry wrote: > On Wed, Oct 14, 2020 at 9:15 AM David Hildenbrand wr= ote: >> >> On 14.10.20 17:22, David Hildenbrand wrote: >>> Hi everybody, >>> >>> Michal Privoznik played with "free page reporting" in QEMU/virtio-bal= loon >>> with hugetlbfs and reported that this results in [1] >>> >>> 1. WARNING: CPU: 13 PID: 2438 at mm/page_counter.c:57 page_counter_un= charge+0x4b/0x5 >>> >>> 2. Any hugetlbfs allocations failing. (I assume because some accounti= ng is wrong) >>> >>> >>> QEMU with free page hinting uses fallocate(FALLOC_FL_PUNCH_HOLE) >>> to discard pages that are reported as free by a VM. The reporting >>> granularity is in pageblock granularity. So when the guest reports >>> 2M chunks, we fallocate(FALLOC_FL_PUNCH_HOLE) one huge page in QEMU. >>> >>> I was also able to reproduce (also with virtio-mem, which similarly >>> uses fallocate(FALLOC_FL_PUNCH_HOLE)) on latest v5.9 >>> (and on v5.7.X from F32). >>> >>> Looks like something with fallocate(FALLOC_FL_PUNCH_HOLE) accounting >>> is broken with cgroups. I did *not* try without cgroups yet. >>> >>> Any ideas? >=20 > Hi David, >=20 > I may be able to dig in and take a look. How do I reproduce this > though? I just fallocate(FALLOC_FL_PUNCH_HOLE) one 2MB page in a > hugetlb region? >=20 Hi Mina, thanks for having a look. I started poking around myself but, being new to cgroup code, I even failed to understand why that code gets triggered though the hugetlb controller isn't even enabled. I assume you at least have to make sure that there is a page populated (MMAP_POPULATE, or read/write it). But I am not sure yet if a single fallocate(FALLOC_FL_PUNCH_HOLE) is sufficient, or if it will require a sequence of populate+discard(punch) (or multi-threading). What definitely makes it trigger is via QEMU qemu-system-x86_64 \ -machine pc-i440fx-4.0,accel=3Dkvm,usb=3Doff,dump-guest-core=3Doff,memory= -backend=3Dpc.ram \ -cpu host,migratable=3Don \ -m 4096 \ -object memory-backend-memfd,id=3Dpc.ram,hugetlb=3Dyes,hugetlbsize=3D2097= 152,size=3D4294967296 \ -overcommit mem-lock=3Doff \ -smp 4,sockets=3D1,dies=3D1,cores=3D2,threads=3D2 \ -nodefaults \ -nographic \ -device virtio-scsi-pci,id=3Dscsi0,bus=3Dpci.0,addr=3D0x4 \ -device virtio-serial-pci,id=3Dvirtio-serial0,bus=3Dpci.0,addr=3D0x5 \ -blockdev '{"driver":"file","filename":"../Fedora-Cloud-Base-32-1.6.x86_6= 4.qcow2","node-name":"libvirt-1-storage","auto-read-only":true,"discard":= "unmap"}' \ -blockdev '{"node-name":"libvirt-1-format","read-only":false,"discard":"u= nmap","driver":"qcow2","file":"libvirt-1-storage","backing":null}' \ -device scsi-hd,bus=3Dscsi0.0,channel=3D0,scsi-id=3D0,lun=3D0,device_id=3D= drive-scsi0-0-0-0,drive=3Dlibvirt-1-format,id=3Dscsi0-0-0-0,bootindex=3D1= \ -chardev stdio,nosignal,id=3Dserial \ -device isa-serial,chardev=3Dserial \ -device virtio-balloon-pci,id=3Dballoon0,bus=3Dpci.0,addr=3D0x7,free-page= -reporting=3Don However, you need a recent QEMU (>=3D v5.1 IIRC) and a recent kernel (>=3D v5.7) inside your guest image. Fedora rawhide qcow2 should do: https://dl.fedoraproject.org/pub/fedora/l= inux/development/rawhide/Cloud/x86_64/images/Fedora-Cloud-Base-Rawhide-20= 201004.n.1.x86_64.qcow2 --=20 Thanks, David / dhildenb