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    Subjectmemcg: cat: memory.memsw.* : Operation not supported
    hi, all

    when I used memory cgroup in latest mainline, the following error occurred:

    # mount -t cgroup -o memory xxx /cgroup/
    # ll /cgroup/memory.memsw.*
    -rw-r--r--. 1 root root 0 Jun 26 23:17 /cgroup/memory.memsw.failcnt
    -rw-r--r--. 1 root root 0 Jun 26 23:17 /cgroup/memory.memsw.limit_in_bytes
    -rw-r--r--. 1 root root 0 Jun 26 23:17 /cgroup/memory.memsw.max_usage_in_bytes
    -r--r--r--. 1 root root 0 Jun 26 23:17 /cgroup/memory.memsw.usage_in_bytes
    # cat /cgroup/memory.memsw.*
    cat: /cgroup/memory.memsw.failcnt: Operation not supported
    cat: /cgroup/memory.memsw.limit_in_bytes: Operation not supported
    cat: /cgroup/memory.memsw.max_usage_in_bytes: Operation not supported
    cat: /cgroup/memory.memsw.usage_in_bytes: Operation not supported

    I'm confusing why it can't read memory.memsw.* files.

    as commit:a42c390cfa0c said, CGROUP_MEM_RES_CTLR_SWAP_ENABLED and
    swapaccount kernel parameter control memcg swap accounting,
    but I confirmed the two options all don't be set:

    # cat /usr/lib/modules/3.5.0-rc4+/source/.config | grep CGROUP_MEM
    CONFIG_CGROUP_MEM_RES_CTLR=y
    CONFIG_CGROUP_MEM_RES_CTLR_SWAP=y
    # CONFIG_CGROUP_MEM_RES_CTLR_SWAP_ENABLED is not set
    CONFIG_CGROUP_MEM_RES_CTLR_KMEM=y
    # cat /proc/cmdline
    BOOT_IMAGE=/vmlinuz-3.5.0-rc4+ root=/dev/mapper/vg_amd--pike--06-lv_root ro rd.lvm.lv=vg_amd-pike-06/lv_swap rd.md=0 LANG=en_US.UTF-8 console=ttyS0,115200n81 KEYTABLE=us SYSFONT=True rd.luks=0 rd.dm=0 rd.lvm.lv=vg_amd-pike-06/lv_root

    so I have two problems here:
    1. when kernel neither set 'CONFIG_CGROUP_MEM_RES_CTLR_SWAP_ENABLED' nor 'swapaccount' options,
    why memcg have memory.memsw.* files ?

    2. why we can't read memory.memsw.* ?

    Addition info:
    when I open CONFIG_CGROUP_MEM_RES_CTLR_SWAP_ENABLED option, the above issues are gone.
    also I tested v3.4.0, there aren't the two issues, so please take a look.

    --
    Thanks,
    Zhouping


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