# [OmniOS-discuss] Omnios: can't start as many kvm's as I thought due to memory pressure

pieter van puymbroeck pietervanpuymbroeck at hotmail.com
Wed Mar 8 19:32:23 UTC 2017

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    Hi,

    I want to start 12 kvm machines in my global zone and I end up in an memlock issue after the 6th machine:

    qemu_mlock: have only locked 0 of 7516192768 bytes; still trying…

    The details:

    # echo "::memstat" | mdb -k

    Page Summary                Pages                MB  %Tot

    ------------     ----------------  ----------------  ----

    Kernel                    1462114              5711    5%

    Boot pages                    166                 0    0%

    ZFS File Data              143529               560    0%

    Anon                        27477               107    0%

    Exec and libs                1244                 4    0%

    Page cache                   4911                19    0%

    Free (cachelist)             3597                14    0%

    Free (freelist)          29809914            116444   95%

    Total                    31452952            122863

    Physical                 31452951            122863

    #

    My pagesize is:

    # pagesize

    4096

    #

    so 31452952 pages = (122863*1024*1024) bytes / 4096 (bytes)

    thus: 31452952 / 256 = 122863MB

    That's correct. So pages to MB we can divide by 256. MB to pages, multiply with 256.

    I want 8GB per vm and I want 12vm's. This is 96GB (98304MB)

    -> needs 98304 * 256 = 25165824 pages.

    31452952 - 25165824 = 6287128 left (or 24559 MB ~ 23.9GB )

    I reserved (in /etc/system ) 15 GB for zfs arc

    15GB = 15360 MB = 3932160 pages

    So this gives 6287128 - 3932160 = 2354968 pages left (or 9199MB ~ 8.98 GB)

    -> this should be sufficient for omnios to run. Unless I'm not aware of other things, which is very well possible.

    So remember

    Page Summary                Pages                MB  %Tot

    ------------     ----------------  ----------------  ----

    ...

    Free (cachelist)             3597                14    0%

    Free (freelist)          29809914            116444   95%

    Total                    31452952            122863

    Physical                 31452951            122863

    #

    Let's boot one kvm with 8GB ram for the vm. We expect to see (8GB *1024) * 256 = 2097152 pages be eaten up. So we should end up with 31452952 - 2097152 = 29355800 pages.

    OR if we are eating from the "Free" part, we should end up with 29809914 - 2097152 = 27712762 pages (or 108252MB ~105.71 GB)

    Let's confirm:

    Before boot:

    # mdb -ke 'availrmem/D ; pages_pp_maximum/D'

    availrmem:

    availrmem:      29845807

    pages_pp_maximum:

    pages_pp_maximum:               1216998

    #

    Boot the machine.

    # echo "::memstat" | mdb -k

    Page Summary                Pages                MB  %Tot

    ------------     ----------------  ----------------  ----

    Kernel                    1472257              5751    5%

    Boot pages                    166                 0    0%

    ZFS File Data              149321               583    0%

    Anon                      2139596              8357    7%

    Exec and libs                1549                 6    0%

    Page cache                   4955                19    0%

    Free (cachelist)             3445                13    0%

    Free (freelist)          27681663            108131   88% <<<----- 27712762 pages

    Total                    31452952            122863

    Physical                 31452951            122863

    # mdb -ke 'availrmem/D ; pages_pp_maximum/D'

    availrmem:

    availrmem:      26621718

    pages_pp_maximum:

    pages_pp_maximum:               1216998

    #

    look there. We expected to end up with 29355800 pages or 27712762 free pages.

    If we check in the available memory 29845807 - 26621718 = 3224089 pages were consumed (12594.09MB ~ 12.29GB )

    Double check: 29809914 - 27681663 = 2128251 pages consumed ( 8313.48MB ~ 8.11GB )

    And this for a machine of 8GB.

    Let's do a test with a vm with 4GB allocated ( 1048576 pages )

    Before boot:

    # echo "::memstat" | mdb -k

    Page Summary                Pages                MB  %Tot

    ------------     ----------------  ----------------  ----

    Kernel                    1476857              5768    5%

    Boot pages                    166                 0    0%

    ZFS File Data              176243               688    1%

    Anon                      2139416              8357    7%

    Exec and libs                1549                 6    0%

    Page cache                   4961                19    0%

    Free (cachelist)             3440                13    0%

    Free (freelist)          27650320            108009   88%

    Total                    31452952            122863

    Physical                 31452951            122863

    # mdb -ke 'availrmem/D ; pages_pp_maximum/D'

    availrmem:

    availrmem:      26596813

    pages_pp_maximum:

    pages_pp_maximum:               1216998

    #

    So we expect

    27650320 - 1048576 = 26601744 free pages (103913.06 MB ~ 101.47 GB free)

    or

    26596813 - 1048576 = 25548237 free pages (99797.80 MB ~ 97.45 GB free)

    Booting the vm.

    And the aftermath:

    # ./start_kvm_pogo.sh

    qemu-system-x86_64: -net vnic,vlan=40,name=net0,ifname=vnic_kvm_pogo0,macaddr=2:8:20:87:2f:69: vnic dhcp disabled

    Started VM: pogo

    VNC available at: host IP 127.0.0.1

    10.0.1.171

    ::1/128

    ::/0 port 5900

    QEMU Monitor, do: # telnet localhost . Note: use Control ] to exit monitor before quit!

    #

    Check the values

    # echo "::memstat" | mdb -k

    Page Summary                Pages                MB  %Tot

    ------------     ----------------  ----------------  ----

    Kernel                    1482301              5790    5%

    Boot pages                    166                 0    0%

    ZFS File Data              180958               706    1%

    Anon                      3198541             12494   10%

    Exec and libs                1549                 6    0%

    Page cache                   4961                19    0%

    Free (cachelist)             3440                13    0%

    Free (freelist)          26581036            103832   85%

    Total                    31452952            122863

    Physical                 31452951            122863

    #

    # mdb -ke 'availrmem/D ; pages_pp_maximum/D'

    availrmem:

    availrmem:      24472324

    pages_pp_maximum:

    pages_pp_maximum:               1216998

    #

    let's verify.

    Test1:

    27650320 - 26581036 = 1069284 pages consumed ( 4176.89 MB ~ 4GB )

    Test 2:

    26596813 - 24472324 = 2124489 pages consumed ( 8298.78 MB ~ 8.10GB )

    3 questions remain.

    - Why does this happen. If we check using the memstat it's fairly ok, but appearently this is not correct as I can't start the 12 machines.

    - How to avoid this. If I say to kvm "use 8GB" I want it to use 8GB not 12GB. Or am I missing something crucial?

    - If it's a (kernel) parameter ... which one and how to set it?

    Thanks and best regards,

    Pieter

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