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I have a debian server and when running "atop 1" the "PAG" row is nearly always red which shows an issue with the paging frequency. Here is an example

PAG | scan  10477 | stall      0 |              | swin       0 | swout     31 |

What can I do to optimize this?

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You have to give us more to go on. What does memory usage look like? What does swap usage look like? Is the server performing well or badly? What does the server do? –  David Schwartz Apr 13 '12 at 8:34
@David Its a server for http file serving with heavy concurrency. Swap is not used. I've lots of free memory 96GB in total. 22 HDDs in a Hardware RAID10. There are big IO-latency spikes causing lots of timeouts even though the outgoing bandwidth is currently just at 300Mbits. –  Philip Apr 13 '12 at 8:48
Oh, okay, then it's perfectly normal. The system is I/O bound. So it's doing as much I/O as it possibly can. The puzzling bit is why you have so much free memory (using more memory should reduce the amount of I/O needed). Are you sure it's really free? Can you post the output of free -m? –  David Schwartz Apr 13 '12 at 8:49
The server is just for storage. The httpd's run on other servers ;-) Here is the output from a storage server with 64GB of ram. As far as I understand it there is currently 62GB available (cached) -> pastebin.com/9wnnJDQs –  Philip Apr 13 '12 at 8:53
Ahh, only a very small amount of RAM is free, 170MB. The vast majority of the RAM is being used as a page cache. That's good and is what you'd expect on an I/O bound server. Sounds normal. Why do you suspect this is a "problem"? –  David Schwartz Apr 13 '12 at 8:56
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