[Linux-cluster] Readhead Issues using cluster-1.01.00

[Velu Erwan]

Velu Erwan a écrit :

> Hi,
> I've been playing with cluster-1.01.00 and I found the reading very slow.
> I've been trying to setup "max_readahead" using gfs_tool and 
> performances are unchanged.
>
I've investigate more on that problem with a collegue.
He founds that gfs is now using a diaper volume.
This volume maps the physical device I provide to gfs, but we had 2 
questions about that :

1°) Why this volume is so big ? On my system it reaches ~8192 ExaBytes !
The first time I saw  that I thought it was an error...

[root at max4 ~]# cat /proc/partitions  | grep  -e "major" -e "diapered"
major minor  #blocks  name
 252     0 9223372036854775807 diapered_g1v1
[root at max4 ~]#


2°) Regarding the source code, this diaper volume never set the 
"gd->queue->backing_dev_info.ra_pages" which is set to zero by
gd->queue = blk_alloc_queue(GFP_KERNEL);
Is it needed to enforce the cache/lock management or is it just a miss ?
This could explain why the reading performances are low while gfs_read() 
makes a generic_file_read() isn't it ?