[Linux-cluster] gfs tuning

[Terry]

On Tue, Jun 17, 2008 at 3:09 PM, Wendy Cheng <s.wendy.cheng at gmail.com> wrote:
> Hi, Terry,
>>
>> I am still seeing some high load averages.  Here is an example of a
>> gfs configuration.  I left statfs_fast off as it would not apply to
>> one of my volumes for an unknown reason.  Not sure that would have
>> helped anyways.  I do, however, feel that reducing scand_secs helped a
>> little:
>>
>
> Sorry I missed scand_secs (was mindless as the brain was mostly occupied by
> day time work).
>
> To simplify the view, glock states include exclusive (write), share (read),
> and not-locked (in reality, there are more). Exclusive lock has to be
> demoted (demote_secs) to share, then to not-locked (another demote_secs)
> before it is scanned (every scand_secs) to get added into reclaim list where
> it can be purged. Between exclusive and share state transition, the file
> contents need to get flushed to disk (to keep file content cluster
> coherent).  All of above assume the file (protected by this glock) is not
> accessed (idle).
>
> You hit an area that GFS normally doesn't perform well. With GFS1 in
> maintenance mode while GFS2 seems to be so far away, ext3 could be a better
> answer. However, before switching, do make sure to test it thoroughly (since
> Ext3 could have the very same issue as well - check out:
> http://marc.info/?l=linux-nfs&m=121362947909974&w=2 ).
>
> Did you look (and test) GFS "nolock" protocol (for single node GFS)? It
> bypasses some locking overhead and can be switched to  DLM in the future
> (just make sure you reserve enough journal space - the rule of thumb is one
> journal per node and know how many nodes you plan to have in the future).
>
> -- Wendy

Good points.  I could try the nolock feature I suppose.  Not quite
clear on how to reserve journal space.  I forgot to post the cpu time,
check out this:

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 4822 root      10  -5     0    0    0 S    1  0.0   2159:15 dlm_recv
 4820 root      10  -5     0    0    0 S    1  0.0 368:09.34 dlm_astd
 4821 root      10  -5     0    0    0 S    0  0.0 153:06.80 dlm_scand
 3659 root      10  -5     0    0    0 S    0  0.0 134:40.14 scsi_wq_4
 4823 root      11  -5     0    0    0 S    1  0.0 109:33.33 dlm_send
  367 root      10  -5     0    0    0 S    0  0.0 103:33.74 kswapd0

gfs_glockd is further below so not so concerned with that right now.
It appears turning on nolock would do the trick.  The times aren't
extremely accurate because I have failed this cluster between nodes
while testing.