[rhelv6-list] Setting overcommit_memory=2 kills system

[Michael Coffman]

On Thu, May 17, 2012 at 1:58 PM, Michael Coffman <
michael.coffman at avagotech.com> wrote:

>
>
> On Thu, May 17, 2012 at 1:26 PM, VINIT ADYA (BLOOMBERG/ 731 LEXIN) <
> vadya at bloomberg.net> wrote:
>
>> Can you post /proc/meminfo.
>>
>
>
Here is meminfo with overcommit_memory=0 and overcommit_ration=50 (defaults)
MemTotal:        2052176 kB
MemFree:         1658912 kB
Buffers:           23036 kB
Cached:           261572 kB
SwapCached:            0 kB
Active:            94208 kB
Inactive:         205604 kB
Active(anon):      20732 kB
Inactive(anon):        4 kB
Active(file):      73476 kB
Inactive(file):   205600 kB
Unevictable:        6216 kB
Mlocked:            6216 kB
SwapTotal:       2052088 kB
SwapFree:        2052088 kB
Dirty:               408 kB
Writeback:             0 kB
AnonPages:         21456 kB
Mapped:            15476 kB
Shmem:               224 kB
Slab:              43392 kB
SReclaimable:      17856 kB
SUnreclaim:        25536 kB
KernelStack:        1048 kB
PageTables:         3292 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:     3078176 kB
Committed_AS:   137197242528 kB
VmallocTotal:   34359738367 kB
VmallocUsed:       13156 kB
VmallocChunk:   34359715924 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



> 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
>



-- 
-MichaelC
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