I need to read through this more thoroughly to get my head around it, but
on my first pass, what jumps out at me is that something significant
_changed_ in terms of "application" behavior with the introduction of ZFS.
I'm saying that that is a bad thing, or a good thing, but it is an
important thing,
and we should try to understand if application behavior will, in general,
change with the introduction of ZFS, so we can advise users accordingly.
Joe appears to be a user of Sun system for some time, with a lot of
experience
deploying Solaris 8 and Solaris 9. He has succesfully deployed systems
without
physical swap, and I understand his reason for doing so. If the
introduction of
Solaris 10 and ZFS means we need to change a system parameter when
transitioning
from S8 or S9, such as configured swap, we need to understand why, and make
sure understand the performance implications.
Why do you think your performance *improves* if you don't use
swap? It is much more likely it *deteriates* because your swap
accumulates stuff you do not use.
I'm not sure what this is saying, but I don't think it came out right.
As I said, I need to do another pass on the information in the messages
to get
a better handle on the observed behviour, but this certainly seems like
something we should explore further.
Watch this space.
/jim
At any rate, I don't think adding swap will fix the problem I am seeing
in that ZFS is not releasing its unused cache when applications need it.
Adding swap might allow the kernel to move it out of memory but when the
system needs it again it will have to swap it back in, and only
performance suffers, no?
Well, you have decided that all application data needs to be memory
resident all of the time; but executables don't need to be (they
are now tossed out on memory shortage) and that ZFS can use less cache
than it wants to.
FWIW, here's the current ::memstat and swap output for my system. The
reserved number is only about 46M or about 2% of RAM. Considering the
box has 3G, I'm willing to sacrifice 2% in the interest of performance.
Page Summary Pages MB %Tot
------------ ---------------- ---------------- ----
Kernel 249927 1952 64%
Anon 34719 271 9%
Exec and libs 2415 18 1%
Page cache 1676 13 0%
Free (cachelist) 11796 92 3%
Free (freelist) 88288 689 23%
Total 388821 3037
Physical 382802 2990
[EMAIL PROTECTED]: swap -s
total: 260008k bytes allocated + 47256k reserved = 307264k used, 381072k
available
So there's 47MB of memory which is not used at all. (Adding swap will
give you 47MB of additional free memory without anything being written
to disk). Execs are also pushed out on shortfall.
There is 265 MB of anon memory and we have no clue how much of it
is used at all; a large percentage is likely unused.
But OTOH, you have sufficient memory on the freelist so there is not
much of an issue.
Casper
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