On Oct 2, 2006, at 2:06 PM, Bob wrote:
On Monday 02 October 2006 09:14, Chuck Swiger wrote:
The swap system knows how to interleave data between the additional swap
areas relatively efficiently,

Yes I discovered that. The additional swap space was instantly used as soon as I activated it; and the added swap improved things measurably. Does the swap system take into account current disk activity when it decides to use a
particular swap?

Sort of. The syncer process runs at idle priority, so normal I/O initiated by your processes will take priority over paging/swapping idle pages of RAM out. There may be additional logic involved to help balance I/O in terms of which swapfile is being used if one drive remains busier than another, but I am not completely familiar with FreeBSD's implementation.

that you need to use more than 2GB of swapspace on a machine with 1GB of
RAM, you should add more RAM, not more swapspace....

It is on order.

The basis for my question about swap priority was based on an observation that the slowdown was due to swapping AND heavy disk usage. I noticed that when snapshots were being made on the main drive (the one I am using all the time), all other processes went to slow-mode. You see, the lack of enough memory caused the system to swap, and it swapped to the heaviest used raid array. I thought if I could force the system to swap to the other raid array (much less used) with the new swapfile, things would improve even more.

Well, you might try benchmarking the system with both arrays used for swapping and with only the less-busy RAID array being used for swapping, and see which one does better.


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