[Lustre-discuss] [zfs-discuss] ZFS/Lustre echo 0 >> max_cached_mb chewing 100% cpu

[Prakash Surya]

On Tue, Oct 22, 2013 at 05:43:31PM +0100, Andrew Holway wrote:
> On 22 October 2013 16:21, Prakash Surya <surya1 at llnl.gov> wrote:
> > This probably belongs on the Lustre mailing list.
> 
> I cross posted :)
> 
> > Regardless, I don't
> > think you want to do that (do you?). It'll prevent any client side
> > caching, and more importantly, I don't think it's a case that's been
> > tested/optimized. What're you trying to acheive?
> 
> Sorry I was not clear, I didn't action this and I cant kill the
> process. It seemed to start directly after running:
> 
> "FSTYPE=zfs /usr/lib64/lustre/tests/llmount.sh"
> 
> I have tried to kill it first with -2 upto -9 but the process will not budge.
> 
> Here is the top lines from perf top
> 
> 37.39%  [osc]              [k] osc_set_info_async
>  27.14%  [lov]              [k] lov_set_info_async
>   4.13%  [kernel]           [k] kfree
>   3.57%  [ptlrpc]           [k] ptlrpc_set_destroy
>   3.14%  [kernel]           [k] mutex_unlock
>   3.10%  [lustre]           [k] ll_wr_max_cached_mb
>   3.00%  [kernel]           [k] mutex_lock
>   2.82%  [ptlrpc]           [k] ptlrpc_prep_set
>   2.52%  [kernel]           [k] __kmalloc

It's probably a bug in the proc handler, resulting in an infinite loop
because it doesn't handle the input "0" well. Since that's not how that
tunable was intended to be used, how about you just don't do that? ;)

Can you open a bug report on this at: https://jira.hpdd.intel.com ?

> 
> Thanks,
> 
> Andrew
> 
> >
> > Also, just curious, where's the CPU time being spent? What process and/or
> > kernel thread? What are the top entries listed when you run "perf top"?
> >
> > --
> > Cheers, Prakash
> >
> > On Tue, Oct 22, 2013 at 12:53:44PM +0100, Andrew Holway wrote:
> >> Hello,
> >>
> >> I have just setup a "toy" lustre setup using this guide here:
> >> http://zfsonlinux.org/lustre and have this process chewing 100% cpu.
> >>
> >> sh -c echo 0 >> /proc/fs/lustre/llite/lustre-ffff88006b0c7c00/max_cached_mb
> >>
> >> Until I get something more beasty I am using my desktop machine with
> >> KVM. Using standard Centos 6.4 with latest kernel. (2.6.32-358.23.2).
> >> my machine has 2GB ram
> >>
> >> Any ideas?
> >>
> >> Thanks,
> >>
> >> Andrew
> >>
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