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.
--
-Chuck
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