[Lustre-discuss] lru_size very small

[Andreas Dilger]

On Aug 22, 2008  15:39 -0400, Brock Palen wrote:
> It looks like lru_size is not a static parameter.  While on most of  
> our hosts it starts as zero.  Once the file system is accessed some  
> the values start to rise.  The values get highest for the MDS.
> 
> cat nobackup-MDT0000-mdc-000001022c433800/lru_size
>   3877

Yes, in 1.6.5 instead of having a static LRU size it is dynamic based
on load.  This optimizes the number of locks available to nodes that
have very different workloads than others (e.g. login/build nodes vs.
compute nodes vs. backup nodes).

> So in 1.6.5.1  are lock dynamically adjusted based on ram available  
> on the MDS/OSS's?  Notice how the value above is _much_ higher than  
> the default '100' in the manual.

The total number of locks available are now a function of the RAM
on the server.  I think the maximum is 50 locks/MB, but this is
hooked into the kernel VM so that in case of too much memory pressure
then the LRU size is shrunk.

> I should point out this value was 0  till I did a   'find . | wc -l'   
> in a directory.  The same is for regular access.  users on nodes that  
> access lustre have locks.  Nodes that have not had lustre access yet  
> are still 0  (by access I mean an application that uses our lustre  
> mount vs our NFS mount.)
> 
> Any feedback on the nature of locks and lru_size?
> We are looking to do what the manual says about upping the number on  
> the login nodes.

Yes, the manual needs an update.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.