cswiger at mac.com
Mon Oct 2 11:23:18 PDT 2006
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
> time), all other processes went to slow-mode. You see, the lack of
> 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
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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