I have a process that is reporting in 'top' that it has 6GB of resident memory and 70GB of virtual memory allocated. The strange thing is that this particular server only has 8GB physical and 35GB of swap space available.
From the 'top' manual:
o: VIRT -- Virtual Image (kb)
The total amount of virtual memory used by the task. It includes
all code, data and shared libraries plus pages that have been
swapped out. (Note: you can define the STATSIZE=1 environment vari-
able and the VIRT will be calculated from the /proc/#/state VmSize
field.)
VIRT = SWAP + RES.
Given this explanation, I would expect the virutal memory allocation for a process to be limited to my swap + physical memory available.
According to 'pmap', the code, shared library, and shared memory sections of this process are all minimal – no more than 300M or so.
Obviously, the machine and the process are still functioning correctly (albeit slowly), so what am I missing here?
Best Answer
It may be demand zero memory which isn't in physical ram, or in the pagefile.
Some resources you may want to look at:
Does your application create a lot of empty memory pages? If so, your application might benefit greatly from:
It allows you to compress and decompress in real-time memory pages. In turn, you are able to keep everything in RAM rather than swap to disk (very slow).