topic Re: mmap kernel tuning in Operating System - HP-UX

mmap kernel tuning

Peter Chegwidden — Tue, 26 Jun 2001 08:06:40 GMT

Can anyone tell me what tunable kernel parameters [e.g. maxdsiz, shmmax etc] would affect the memory available to the mmap() function?
I have a situation where I can get a total of approx. 1035MB of shared mmap()'ed memory, albeit only when allocated by a number of individual processes i.e.

proc 1 - 220MB
proc 2 - 190MB
proc 3 - 325MB
proc 4 - 300MB

I can get a further 300MB by allocating smaller amounts of memory [e.g. 50 - 100MB] by more processes.
Is there a system [HP-UX] imposed limit on the amount of mmap'ed memory available?
Are there limits imposed on a per process or controlling process basis, and does this limit apply to descendants [child processes]?
Am I only able to get the further 300MB in smaller chunks due to free memory fragmentation or is there another reason?

Info.: The above results were achieved with shmmax at 0x40000000 [1 GB] and maxdsiz at 0x20000000 [0.5 GB]

Thanks in anticipation.

Peter

Re: mmap kernel tuning

Magdi KAMAL — Tue, 26 Jun 2001 11:43:16 GMT

Hi,

You may find what you need in the attached man file.

Increase the swap space may resolve process competing on space.

Re: mmap kernel tuning

AlHassani Mohamed — Tue, 26 Jun 2001 13:16:46 GMT

Hi Kamal,
this is depending from the Operating System whitch you are using.
you can only using 1.75 GB shared memory (shmmax) for HPUX 10.20 an 11.0 32 Bit.
If you are using 11.0 64 Bit OS, then can you can increase the parameter shmmax to 16 GB. But it is nessesary to increasing the swap sapce to 20 GB.
to obtain which kernel you are using in 11.0, you can use the command getconf Kernel_BITS.

Regards
Mohamed

Re: mmap kernel tuning

Peter Chegwidden — Wed, 27 Jun 2001 11:30:42 GMT

Thanks Kamal and Mohamed.
Kamal,
I was unable to read the attachment, but assume that it was the mmap man page [man mmap] on HP_UX 11. I had already looked at this, but unfortunately it did not provide the specific info I need.
The swap space is at 17GB with approx. 14GB available.

Mohamed,
Does the 1.75GB limit apply to 32 bit apps. running on a 64 bit kernel?

Again, many thanks to you both. This is my 1st posting to this forum, and I am very impressed with the response.

Peter