[Lustre-discuss] Lustre 2.0 client cache size

[Andreas Dilger]

On 2011-03-17, at 6:37 AM, DEGREMONT Aurelien wrote:
> I'm trying to control the amount of cache memory used by Lustre clients 
> with Lustre 2.0
> There is a /proc tuning called "max_cache_mb" in llite which is 
> documented in Lustre manual.
> Unfortunately, after testing it and checking the source code it seems 
> this variable is present but it not used anymore in Lustre code.
> This is not the case in 1.8.
> 
> I did not find if this was removed or this was partially included in 
> Lustre 2.0.
> What's the current status of this and how can I tell to my client to 
> avoid caching too many data?

The client VM usage was one of the areas that was completely rewritten by Nikita for 2.0, so it was likely this functionality was lost at that time.  I don't have any idea at this time how hard it would be to restore.

> Those clients do a lot of read and write in Lustre filesystems but 
> thoses files will not be re-read soon, so it is useless to fill memory 
> with it. Moreover, when the client memory is full, Lustre performance 
> are really impacted.

It may be possible to use fadvise(FADV_NOREUSE) from the application to cause the VM to discard these pages after the first use.

Cheers, Andreas
--
Andreas Dilger 
Principal Engineer
Whamcloud, Inc.