how to reduce the memory used by sys

[darrel chen]

Hi,

our environment is hpux11.23 based-on Itanium, when i used glance to monitor the performance, i found almost 1.2 GB memory used by os itself, so why os used so many memory and how can reduce it?

Thanks
Darrel

[Stuart A Jaskowiak]

I don't have an HP-UX box handy to test with, but 9 times out of 10 if the memory in a server isn't being used for active processes, it gets assigned to disk cache.

Add some load to your system, i.e. run a few processes, and see if that number goes down or not.

[spex]

Hi Darrel,

You could decrease certain kernel tunables, such as those that control the size of system tables (e.g. nproc or nfiles), and then recompile your kernel and reboot. However, 1.2GB for 11iv2 on Itanium seems quite acceptable. In fact, to improve performance, you may want to _increase_ certain kernel parameters, thereby increasing system memory usage.

If you're experiencing a RAM crunch, check if you have a dynamic buffer cache enabled. If so, make it static by setting dbc_max_pct = dbc_min_pct. Then steal memory from it.

http://docs.hp.com/en/B8725-90103/ch12s03.html

PCS

[Bill Hassell]

1.2 Gb is quite normal for 11.23 on Itanium. If you are running out of RAM, look at the buffer cache or get a lot more RAM. There is very little you can do to change kernel parameters to reduce kernel RAM usage and not make the system unusable. 4 Gb is pretty small for many database products like Oracle.

[darrel chen]

thanks lot. I know it's not a big issue, but in hpux11i, usually sys memory is lower than 500MB, so i'm just wondering why Itanium use so much memory, do you think it's possible that because 'swapmem_on', seems with it open os will set aside some memory for swap, do you have any idea about how swapmem_on works and how much memory it will cost?

Darrel

[darrel chen]

Hi Bill, by the way, how do you know our physical memory is 4GB, is there any relationship between 'sys memory' and 'phy memory'?

Darrel

[Bill Hassell · Accepted solution]

> thanks lot. I know it's not a big issue, but in hpux11i, usually sys memory is lower than 500MB, so i'm just wondering why Itanium use so much memory...

This is quite normal for Itanium boxes. Comparing the two very different architectures is not useful.

> do you think it's possible that because 'swapmem_on', seems with it open os will set aside some memory for swap, do you have any idea about how swapmem_on works and how much memory it will cost?

No, the kernel does not use any local RAM for swapmem_on. Swapmem_on is a technique to reduce unused swap space. When swapmem_on=0, then the kernel requires every process to have swap reserved. So 4Gb of RAM with 1Gb of swap means that nothing will run beyond the 1Gb swap space. Set swapmem_on=1 and now up to 75% of total RAM can have processes running without any swap reservation -- the 1Gb swap space is now in addition to the 75% of RAM.

> Hi Bill, by the way, how do you know our physical memory is 4GB, is there any relationship between 'sys memory' and 'phy memory'?

That was just a guess. There is no direct relationship between kernel memory and physical memory. A system with 64Gb of RAM can have a kernel with 1.2 Gb system memory. However, with that much RAM, it is likelt that several system tables like nproc and nfile are significantly larger which will increase the kernel space. For Itanium kernels, you can expect about them to occupy about twice as much RAM given similar kernel parameters and drivers.

[darrel chen]

Thanks Bill, now, I totally understand what's happening in our system, you are amazing. I really appreciate it. Merry Christmas.