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a lot of paging in/out - What is it?

Hi experts,

I am jumping via google from one page to another one and I am still not sure what paging is and what I am looking for 🤯

What I got is, that paging is working differently to swapping and just storing parts of a process on the disc.

Hopefully this is correct.


But what is not, page-in, page-out and faults?
Does it mean the following:

- page-in, bringing the pages from memory to disc

- page-out, bringing the page out of the disc

- faults, bringing the page back to memory as it was requested?

Next item is, in "sar -b" i find values like 13318 pgpgin/s.

We have pagesize 4096, so this means weave a paging-in from around 53272 kb/s.

But what means /s? Is it an average or total value? I can't imagine that the system would page 53 MB per second.

Next questions, why is it paging, when still a lot of memory is available?

Kind regards

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  • Best Answer
    Posted on Aug 04, 2015 at 12:13 PM

    Hi Christian,

    To summarize what it means, your computer has a certain amount of RAM, which is its "memory". It simulates more RAM by allowing extra data to be saved to the hard disk, which is known as Virtual Memory. To do this, it breaks your memory space up into "pages". Applications that need access to data that is in memory call the data by page. If an application calls a page and it is in the RAM, then it is a "page in" occurs. If an app calls for a page from memory, and that page is currently stored on the hard disk and has to be read back into the RAM, then a "Page Out" occurs. A "Page-out" slows the operation of the system down because it has to read the data from a hard disk into RAM first, rather than reading straight from the RAM. If page-outs exceed page-ins, you definitely don't have enough RAM.

    Writing memory pages to the page file when there is still plenty of RAM is a good thing. As soon as a program requests more memory than there is free, the OS can start clearing out space as soon as possible. Better to prepare now than later. If the OS were to wait around, then you run into a performance bottleneck. If a program asks for more memory than is available, now you have to wait until the OS writes out changed memory block, and then free them up.

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