Messages in this thread | | | Subject | Re: [RFC PATCH 1/8] mm: mmap: unmap large mapping by section | From | Yang Shi <> | Date | Wed, 21 Mar 2018 10:16:41 -0700 |
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On 3/21/18 9:50 AM, Yang Shi wrote: > > > On 3/21/18 6:14 AM, Michal Hocko wrote: >> 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.
BTW, this is not the only place to acquire mmap_sem in proc_pid_cmdline_read(), it calls access_remote_vm() which need acquire mmap_sem too, so the mmap_sem scalability issue will be hit sooner or later.
Yang
> > Actually, Alexey Dobriyan had the same comment when he reviewed my > very first patch (which changes down_read to down_read_killable at > that place). > > Those 4 values might be changed by prctl_set_mm() and > prctl_set_mm_map() concurrently. They used to use down_read() to > protect the change, but it looks not good enough to protect concurrent > writing. So, Mateusz Guzik's commit > ddf1d398e517e660207e2c807f76a90df543a217 ("prctl: take mmap sem for > writing to protect against others") change it to down_write(). > > It seems mmap_sem can be replaced to a dedicated lock. How about > defining a rwlock in mm_struct to protect those data? I will come up > with a RFC patch for this. > > However, this dedicated lock just can work around this specific case. > I believe solving mmap_sem scalability issue aimed by the patch series > is still our consensus. > > Thanks, > Yang > > > >
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