[Orca-users] Re: Memory Usage Graphs

[Darren Dunham]

> 
> Liston Bias <list2002 at bias.org> probably said:
> > I am guessing that the way Solaris 8 handles memory & paging is
> > mucho different from Solaris 8 and thus the graphs may be incorrect
> > for 8.  Does this assumption have merit or does Solaris 8 just
> > handle it much better giving me more free memory.

Considerably different.

> Solaris 8 has the "priority paging" method as a default, whereas you
> needed to specificly enable it for a patched 2.6 box or a Solaris 7
> box.

While many of the benefits of "priority paging" are combined into the
Solaris 8 memory management, they are not really the same at all.

The big "problem" with 7 and earlier is that memory used for disk
caching counted against the free list.  The means that simply doing I/O
had the effect of making the box appear to be out of memory, and it
causes the page scanner to kick in to get more free memory.

Priority paging is a nice attempt at an improvement.  It allows the page
scanner, when it kicks in at the lowest level, to not free executable
pages.  That usually means that it flushes disk cache in preference to
other pages.   Pretty good.

Solaris 8+ now maintains a separate list of disk cache pages.  The page
scanner *never* kicks in to free them, and they don't show up to make
the free list appear small.  So now instead of a few megabytes free no
matter what, your box should now show memory use corresponding only to
running programs and allocated memory.

Because of this, your "free memory" graphs will appear very different
between the two.  Prior to 8, it was difficult to tell when a box was
out of memory.  You could look at the page scanner and try to guess, but
that's all it really was.  Either low memory or high I/O rates could
drive the scanner high.

Now you can look at the free memory and actually get some information
out of it.  The page scanner should now kick in *only* if you are truly
out of memory.


-- 
Darren Dunham                                           ddunham at taos.com
Unix System Administrator                    Taos - The SysAdmin Company
Got some Dr Pepper?                           San Francisco, CA bay area
         < This line left intentionally blank to confuse you. >