Comments on: Making the GUI faster in Ubuntu Linux

By: tyler

tyler — Tue, 10 Aug 2010 13:23:46 +0000

Thanks, Alan. That’s very helpful. I do a lot with BackupPC. If you have a chance to rebuild this server or replace it, you will be much happier with performance under RAID10. I recently built an identical machine to my backup server, except that it had 4x 1TB disks in RAID-10 configuration instead of 5x 500GB disks in RAID-5. I cloned the BackupPC filesystem to it, and started backups on it. Backups now finish 40% faster and I can run 25% more of them, simultaneously.

By: Alan

Alan — Tue, 10 Aug 2010 12:54:34 +0000

In our case I wanted to get file system caches out of RAM! Setting the vfs_cache_pressure parameter to a value greater than 100 will tell the kernel to more actively reclaim RAM used by caches. A backup server of ours was swapping heavily, regardless of having 2 gigs of physical RAM and very few applications running.

I guess file caches being read into RAM were to blame, as the server is actively using rsync to backup about 25 workstations in our small office. The disk thrashing was very heavy, and I found this to resolve the problems:

sysctl -w vm.swappiness=20
* Tell the kernel to swap applications out of RAM less (give preference to code rather than data from caches). Might not have done as much to remedy the problem as the other settings below, default is 60 and I might switch back after monitoring.

sysctl -w vm.vfs_cache_pressure=10000
* Tell the kernel to reclaim physical RAM used by file system caches more often. Default setting is 100.

sysctl -w vm.dirty_ratio=2
* Tell the kernel to keep the dirty page / physical RAM ratio lower, 2%. Default is 10.

sysctl -w vm.dirty_background_ratio=1
* Tell the kernel to start swapping dirty pages out as soon as they hit 1% (start flushing out early, before hitting the above ratio)

Hope this helps someone. For reference, our server is Ubuntu 9.04, kernel 2.6.33, using BackupPC and an ext3 RAID5 (md).

By: Hayde

Hayde — Sun, 08 Feb 2009 15:46:29 +0000

Dear sir,

Kindly, I need to make setting for cache in ubuntu , im make some command but the cache don’t become active .

Please learn me about these command if possible my friend ….

I’ll wait you ….

Best Regards.
–
Hayder.

By: tyler

tyler — Mon, 13 Oct 2008 11:54:15 +0000

Oops. I miswrote. Either run those two lines, or put the entries in without “sysctl -w”. I’ll edit the entry shortly.

By: Adam

Adam — Mon, 13 Oct 2008 10:44:36 +0000

When I copy those lines verbatim I get:

root@apu:/etc# sysctl -p
error: “sysctl -w vm.swappiness” is an unknown key
error: “sysctl -w vm.vfs_cache_pressure” is an unknown key

I presume it should be:

vm.swappiness=1
vm.vfs_cache_pressure=50

I’m still opening and closing windows trying to see if I notice a difference.