[Cc Vladimir]
On Wed 14-11-18 15:09:09, Baoquan He wrote:
> Hi,
>
> Tested memory hotplug on a bare metal system, hot removing always
> trigger a lock. Usually need hot plug/unplug several times, then the hot
> removing will hang there at the last block. Surely with memory pressure
> added by executing "stress -m 200".
>
> Will attach the log partly. Any idea or suggestion, appreciated.
>
[...]
> [ +0.007169] Not tainted 4.20.0-rc2+ #4
> [ +0.004630] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [ +0.008001] kworker/181:1 D 0 1187 2 0x80000000
> [ +0.005711] Workqueue: memcg_kmem_cache memcg_kmem_cache_create_func
> [ +0.006467] Call Trace:
> [ +0.002591] ? __schedule+0x24e/0x880
> [ +0.004995] schedule+0x28/0x80
> [ +0.003380] rwsem_down_read_failed+0x103/0x190
> [ +0.006528] call_rwsem_down_read_failed+0x14/0x30
> [ +0.004937] __percpu_down_read+0x4f/0x80
> [ +0.004204] get_online_mems+0x2d/0x30
> [ +0.003871] memcg_create_kmem_cache+0x1b/0x120
> [ +0.004740] memcg_kmem_cache_create_func+0x1b/0x60
> [ +0.004986] process_one_work+0x1a1/0x3a0
> [ +0.004255] worker_thread+0x30/0x380
> [ +0.003764] ? drain_workqueue+0x120/0x120
> [ +0.004238] kthread+0x112/0x130
> [ +0.003320] ? kthread_park+0x80/0x80
> [ +0.003796] ret_from_fork+0x35/0x40
For a quick context. We do hold the exclusive mem hotplug lock
throughout the whole offlining and that can take quite some time.
So I am wondering whether we absolutely have to take the shared lock
in this path (introduced by 03afc0e25f7f ("slab: get_online_mems for
kmem_cache_{create,destroy,shrink}")). Is there any way to relax this
requirement? E.g. nodes stay around even when they are completely
offline. Does that help?
--
Michal Hocko
SUSE Labs
