[ILUG] ftp.heanet.ie

[Colm MacCarthaigh]

On Wed, Jan 07, 2004 at 07:02:57AM -0800, Rick Moen wrote:
> When you have time (obviously not now!), I'd be fascinated and grateful
> to hear details of how you tune the 2.6 VM.  Thanks!

It's a lot of guesswork, voodoo incantations, searching of mailing list
archives, reading source, and reading Mel's documentation, In this case,
where we're at now (and it's moving target as we monitor the system)
I have;

fs/xfs/refcache_size = 512
vm/min_free_kbytes = 512000
vm/lower_zone_protection = 1024
vm/page-cluster = 5
vm/swappiness = 100

in /etc/sysctl.conf, as usual everything is relative to /proc/sys. The
XFS refcache is just to cache more inodes, metadata and the like, help
us a lot. I have min_free_kbytes set to half a gig of Ram, that may
sound like an awful lot, but it's not really - a single rsync or mirror
process can frequently try to nab that much in one go on us.

lower_zone_protection is very important, because when you have 12Gb
of ram, the structures used to reference memory itself can start
taking up most of the IO'able space on you, I've tolk the VM to
try and keep a gig floating around, rather than have to swap
insanely.

page-cluster is 5 , instead of 3, so that when the system does get tight
on ram, we can remedy the situation as quickly as possible, and swap
more pages more quickly. 

Swappiness is freaky, it's default for me is 60, I'm bumped it to
100, because I'd prefer to see memory swapped than run out of IOable
memory, it's seems to have helped do the trick for now anyway.

-- 
Colm MacCárthaigh                        Public Key: colm+pgp at stdlib.net