Hello,
In general I am in the habit of turning off memory overcommit because I
believe it's a bad thing in a multi-user environment. This was never a
problem on rhel5 systems, but on rhel6, I am having issues. When I try
to set overcommit_memory=2, my system locks up. It basically behaves as
if the memory is all used up... I see the same behavior on centos6 or
rhel6. Following is some output from each platform.
# -- RHEL6
# uname -a
Linux joker 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011 x86_64
x86_64 x86_64 GNU/Linux
#lsb_release -a
LSB Version:
:core-4.0-amd64:core-4.0-noarch:graphics-4.0-amd64:graphics-4.0-noarch:printing-4.0-amd64:printing-4.0-noarch
Distributor ID: RedHatEnterpriseWorkstation
Description: Red Hat Enterprise Linux Workstation release 6.2 (Santiago)
Release: 6.2
Codename: Santiago
# free
total used free shared buffers cached
Mem: 2052176 234828 1817348 0 15352 112852
-/+ buffers/cache: 106624 1945552
Swap: 2052088 0 2052088
# sysctl -a |grep commit
vm.overcommit_memory = 0
vm.overcommit_ratio = 50
vm.nr_overcommit_hugepages = 0
# sysctl -w vm.overcommit_memory=2
vm.overcommit_memory = 2
# ls
-bash: fork: Cannot allocate memory
#
#--- CENTOS6 --------------------------
# uname
-a
Linux joker 2.6.32-220.el6.x86_64 #1 SMP Tue Dec 6 19:48:22 GMT 2011 x86_64
x86_64 x86_64 GNU/Linux
# lsb_release -a
LSB Version:
:core-4.0-amd64:core-4.0-noarch:graphics-4.0-amd64:graphics-4.0-noarch:printing-4.0-amd64:printing-4.0-noarch
Distributor ID: CentOS
Description: CentOS release 6.2 (Final)
Release: 6.2
Codename: Final
# free
total used free shared buffers cached
Mem: 2052176 378668 1673508 0 19472 252576
-/+ buffers/cache: 106620 1945556
Swap: 2052088 0 2052088
# sysctl -a |grep commit
vm.overcommit_memory = 0
vm.overcommit_ratio = 50
vm.nr_overcommit_hugepages = 0
# sysctl -w vm.overcommit_memory=2
vm.overcommit_memory = 2
[root at joker ~]# ls
-bash: fork: Cannot allocate memory
One last point. If I set the overcommit values in /etc/sysctl.conf and
then reboot, the values get set correctly on boot and everything seems
fine. In addition I can then change the value of overcommit_memory to 0
and back to 2 with out any ill affects.
Searches for issues with setting overcommit_memory=2 haven't turned up
anything useful..
Thanks.
--
-MichaelC