Strange "Page Outs" Question

[knoxtown]

Hey everyone, sorry if this is a stupid question, but its been bugging me all day.

My understanding of the Activity Monitor is that Page Outs refers to the system using HD space when it uses all available RAM, correct?

If that's the case, take a look at the screenshot I've posted. I'm sitting with 17 GB free RAM, and it shows page outs...

Anyway, it's obviously not a big deal, but just hoping someone can de-stupify me.

Btw, its a 2012 27" i7 iMac if that matters for some reason.

[leman]

Originally Posted by knoxtown

My understanding of the Activity Monitor is that Page Outs refers to the system using HD space when it uses all available RAM, correct?

Not exactly. A page out occurs when an application tries to access some data in the RAM, but for some reason this data is not there. Usually (and you are right here) this happens when there is a shortage of available RAM and the OS offloads some data in the RAM to the disk in order to accomodate for this shortage. However, it can also happen under different circumstances. E.g. when the application uses certain APIs (e.g. file mapping) or when some data is accessed so infrequently that the OS will offload it even without a RAM shortage.

Originally Posted by knoxtown

If that's the case, take a look at the screenshot I've posted. I'm sitting with 17 GB free RAM, and it shows page outs...

The page-in/page-out statistics are cumulative since your last computer restart. Right now you might have 17Gb free RAM, but maybe you were doing something very RAM-intensive yesterday. Anyway, your page-outs are less than 4% of the total RAM access. Nothing to worry about here!

[knoxtown]

Originally Posted by leman

Not exactly. A page out occurs when an application tries to access some data in the RAM, but for some reason this data is not there. Usually (and you are right here) this happens when there is a shortage of available RAM and the OS offloads some data in the RAM to the disk in order to accomodate for this shortage. However, it can also happen under different circumstances. E.g. when the application uses certain APIs (e.g. file mapping) or when some data is accessed so infrequently that the OS will offload it even without a RAM shortage.



The page-in/page-out statistics are cumulative since your last computer restart. Right now you might have 17Gb free RAM, but maybe you were doing something very RAM-intensive yesterday. Anyway, your page-outs are less than 4% of the total RAM access. Nothing to worry about here!

Now I know! Thanks for clarifying that for me!