[RealMadrid]

Hi!

Just curious. When I look at the terminal I see that there are no pageouts what seems logical as I have 1GB Ram and do not open to many apps at once. But there are always pageins. I must have understood something wrong because I thought a pageout happens when there in not enough Ram. Some memory gets written to disk and other is loaded from disk. But then how can the system load information that hasn´t been previously written to disk?

Thanks.

[proton]

In Unix operating systems you can "map" a file into memory. This means that a chunk of memory is allcoated and is marked as having the contents as what is on disk in a certain location, but it does not copy that data directly into memory.

This means you've now got some memory allocated, with data on disk that must be paged in, and yet nothing has been paged out to disk. So, obviosuly, if you want to use that data you have to page in data from disk to use it.

One of the ways of mapping files into memory is the mmap(2) system call for those interested in looking around.

- proton

[RealMadrid]

Ok. Thanks!

Some my error was to think that paging is only done to allocate more "memory" but it can also be used as a type of cache for file access.

[nereus]

also, remember that many unix systems (probably, but I'm not sure, including OS X) use such a system to get programs in.

That is, when you start a process, the system maps the executable, then says go. On "go", the system says, "wait, that memory's not in, I'll go page it in." And off we go...