Mediate disk io with ionice

http://blog.prgmr.com/xenophobia/2008/06/using-ionice1-to-mediate-disk.html

first, find the heavy user with iostat or the like.

this will give you a device mapper name. dm-xx

xx is the minor number you see in ls -l /dev/mapper

[root@chariot ~]# ls -l /dev/mapper|grep " 51 "
brw-rw---- 1 root disk 252, 51 Sep 11 23:22 guests-lvname

Then find the lvname in /etc/xen

grep lvname /etc/xen/*
/etc/xen/username:	'phy:/dev/guests/lvname,xvda,w',

First, look at the console. Is it spinning on an oom-kiler? in that case, it's probably alrealdy messed up for the user, so just reboot it.

Next, if it's okay, they are just using a lot of I/O, you can make I/O only suck for them with ionice.

look up the domain ID now, in this case, it's 52

[root@chariot ~]# xm list username
Name                                        ID   Mem VCPUs      State   Time(s)
weightech                                   52  1024     2     -b---- 454832.8

[root@chariot ~]# ps ax |grep blkback.52.xvd
 2745 ?        S<     1:54 [blkback.52.xvda]
 2746 ?        S<     0:00 [blkback.52.xvde]
 2747 ?        S<     0:00 [blkback.52.xvdf]
26608 pts/9    R+     0:00 grep blkback.52.xvd
[root@chariot ~]# 

in my case, almost everything is xvda.

[root@chariot ~]# ionice -p 2745 -c 2 -n 7

limited, I think? it only kinda works.

[root@chariot ~]# ionice -p 2745 -c 3

now, it's really limited. Note, it sucks to be that guest, but that guest was making it suck for everyone else, so we need a better policy on this.