[rhelv6-list] Setting overcommit_memory=2 kills system

[Michael Coffman]

On Thu, May 17, 2012 at 1:26 PM, VINIT ADYA (BLOOMBERG/ 731 LEXIN) <
vadya at bloomberg.net> wrote:

> Can you post /proc/meminfo.
>

This is after the system has been rebooted with overcommit turned off.
Not sure if that matters:

[root at joker ~]# cat /proc/meminfo
MemTotal:        2052176 kB
MemFree:         1657152 kB
Buffers:           20160 kB
Cached:           254396 kB
SwapCached:            0 kB
Active:           126156 kB
Inactive:         174860 kB
Active(anon):      31988 kB
Inactive(anon):        8 kB
Active(file):      94168 kB
Inactive(file):   174852 kB
Unevictable:        6216 kB
Mlocked:            6216 kB
SwapTotal:       2052088 kB
SwapFree:        2052088 kB
Dirty:               188 kB
Writeback:             0 kB
AnonPages:         32588 kB
Mapped:            16740 kB
Shmem:               228 kB
Slab:              43436 kB
SReclaimable:      17768 kB
SUnreclaim:        25668 kB
KernelStack:        1080 kB
PageTables:         3680 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:     4063220 kB
Committed_AS:     125088 kB
VmallocTotal:   34359738367 kB
VmallocUsed:       13156 kB
VmallocChunk:   34359715916 kB
HardwareCorrupted:     0 kB
AnonHugePages:         0 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:        6148 kB
DirectMap2M:     2088960 kB


> ----- Original Message -----
> From: michael.coffman at avagotech.com
> To: centos at centos.org, rhelv6-list at redhat.com
> At:  5/17 15:12:12
>
> 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
>



-- 
-MichaelC
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listman.redhat.com/archives/rhelv6-list/attachments/20120517/3f51b48c/attachment.htm>