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тАО07-17-2008 03:37 AM
тАО07-17-2008 03:37 AM
LowFree Memory
We have an issue with a Redhat AS3 UPD8 server that is exhausting LowFree memory. Once this happens the OOM killer kicks in and wrecks havoc with arbitary processes. I can see LowFree dropping over time, but don't understand what's grabbing it and why it is not being released. I don't believe that we have a physical memory problem - there is 10Gb allocated to the VMWare installation and the application doesn't use all of that anyway. There is no swap activity. We are using the 32Bit snmp kernel. We cant upgrade the Redhat installation, and as it's on VMWare we cannot (apparently) use the HugeMem kernel.
Any ideas?
Any ideas?
3 REPLIES 3
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тАО07-17-2008 05:29 AM
тАО07-17-2008 05:29 AM
Re: LowFree Memory
Shalom,
Work with the application to reduce memory use.
Look for memory leaks.
http://www.hpux.ws/?p=8
Works for Linux and HP-UX
SEP
Work with the application to reduce memory use.
Look for memory leaks.
http://www.hpux.ws/?p=8
Works for Linux and HP-UX
SEP
Steven E Protter
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com
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тАО07-17-2008 05:50 AM
тАО07-17-2008 05:50 AM
Re: LowFree Memory
The 32-bit kernel can directly access only 4 GB of memory. With special PAE tricks, you can use more than 4 GB with a 32-bit kernel, but there are certain limitations:
- The total memory usage of any one process may not exceed 4 GB (in practice the limit is even lower).
- to transfer data between processes, the system must use a "bounce buffer" which must be located in the bottom 4GB area
- DMA transfers must be targetted to "bounce buffers" in the bottom 4 GB too.
- the use of PAE causes some performance degradation
In short, in 32-bit machines, there are many things that require "low" memory, so it can easily become a bottleneck.
Is the application transferring large amounts of data from/to disks? (DMA transfers)
MK
- The total memory usage of any one process may not exceed 4 GB (in practice the limit is even lower).
- to transfer data between processes, the system must use a "bounce buffer" which must be located in the bottom 4GB area
- DMA transfers must be targetted to "bounce buffers" in the bottom 4 GB too.
- the use of PAE causes some performance degradation
In short, in 32-bit machines, there are many things that require "low" memory, so it can easily become a bottleneck.
Is the application transferring large amounts of data from/to disks? (DMA transfers)
MK
MK
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тАО08-01-2008 10:39 PM
тАО08-01-2008 10:39 PM
Re: LowFree Memory
work with app team to lower memory consumption :) lol
Not sure why you can't run hugemem kernel on vmware, that is a solution, so I would try using the hugemem kernel at all costs.
Otherwise, you can add in lower_zone_protection:
echo "250" > /proc/sys/vm/lower_zone_protection
add to /etc/sysctl.conf
vm.lower_zone_protection = 250
only other resolution is running 64 bit, if you can't run the hugemem kernel.
Not sure why you can't run hugemem kernel on vmware, that is a solution, so I would try using the hugemem kernel at all costs.
Otherwise, you can add in lower_zone_protection:
echo "250" > /proc/sys/vm/lower_zone_protection
add to /etc/sysctl.conf
vm.lower_zone_protection = 250
only other resolution is running 64 bit, if you can't run the hugemem kernel.
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