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On my macbook air I noticed a weird problem, I wonder if this is normal.

I was copying 4gb file from my mac to home server using scp.

First I noticed my usb/wireless mouse getting sluggish I checked MBA trackpad and it seemed fine.

Afterwards I noticed ram was at 95% (4gb) I purged ram which brought it back to 32% which is normal for my system. After few seconds I see it slowly crawl back to 89% and increasing.

Any ideas what is happening? is something wrong with ram sticks? or is this normal behavior with SCP. I thought about it a little, and considering that scp is a secure copy probably there is some kind of encrypting going on on my end and since it was 4gb file probably system was stressed for increased amount of time (but this doesn't hold as CPU was 20-30%).

At this moment ram is at 99%.

checked with ubuntu home server and same situation free ram 66mb and rest of 2gb ram stick is wired.

I also want to mention that most of the ram on my mac is also inactive just wired. My only annoyance is mouse sluggishness at this point.

any thoughts?

share|improve this question
What sort of network connection are you using for this scp session? Any chance it's related to USB? – user3463 Jul 13 '12 at 19:39
@RandolphWest I used wifi network. No usb dongle. – Sandro Dzneladze Jul 15 '12 at 17:48
up vote 1 down vote accepted

Methinks you're confused how memory is used and allocated.

Unused ram is wasted ram, the system should cache files and data automatically as needed to speed accessess, dumping the cached data if a program needs more memory.

You need to look at what the ram is being used for, often it's a small portion for programs and a huge portion for caching done by the system.

The usage you're seeing is likely the system caching the data scp reads from the drive. It was dumped when you 'purged ram' (?), and slowly built up again as scp continued.

On a sorta related note, I'd recommend using rsync instead of scp, it'll only copy what has changed, and uses compression to speed the data transfer (if possible).

share|improve this answer
How does this explain the USB slowdown? – user3463 Jul 15 '12 at 17:49
Ummm, ... high system interrupt load? ionice -c3 ... may help. don't know. – lornix Jul 15 '12 at 18:37

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