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    SubjectRe: [RFC PATCH 1/8] mm: mmap: unmap large mapping by section
    On Wed 21-03-18 05:31:19, Yang Shi wrote:
    > When running some mmap/munmap scalability tests with large memory (i.e.
    > > 300GB), the below hung task issue may happen occasionally.
    >
    > INFO: task ps:14018 blocked for more than 120 seconds.
    > Tainted: G E 4.9.79-009.ali3000.alios7.x86_64 #1
    > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
    > message.
    > ps D 0 14018 1 0x00000004
    > ffff885582f84000 ffff885e8682f000 ffff880972943000 ffff885ebf499bc0
    > ffff8828ee120000 ffffc900349bfca8 ffffffff817154d0 0000000000000040
    > 00ffffff812f872a ffff885ebf499bc0 024000d000948300 ffff880972943000
    > Call Trace:
    > [<ffffffff817154d0>] ? __schedule+0x250/0x730
    > [<ffffffff817159e6>] schedule+0x36/0x80
    > [<ffffffff81718560>] rwsem_down_read_failed+0xf0/0x150
    > [<ffffffff81390a28>] call_rwsem_down_read_failed+0x18/0x30
    > [<ffffffff81717db0>] down_read+0x20/0x40
    > [<ffffffff812b9439>] proc_pid_cmdline_read+0xd9/0x4e0

    Slightly off-topic:
    Btw. this sucks as well. Do we really need to take mmap_sem here? Do any
    of
    arg_start = mm->arg_start;
    arg_end = mm->arg_end;
    env_start = mm->env_start;
    env_end = mm->env_end;

    change after exec or while the pid is already visible in proc? If yes
    maybe we can use a dedicated lock.
    --
    Michal Hocko
    SUSE Labs

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