"top" display on FreeBSD
Americart
I have a question about system memory in a Xeon/FreeBSD 3.1 system.
Here's my "top" display:
Mem: 35M Active, 362M Inact, 46M Wired, 8349K Buf, 60M Free
Swap: 1024M Total, 1024M Free
Notice that there's no mention of cache. Another user recently posted
their 3.1 "top" display, and it DOES show cache:
Mem: 160M Active, 36M Inact, 35M Wired, 12M Cache, 8344K Buf, 5572K Free
Swap: 570M Total, 55M Used, 516M Free, 10% Inuse
My questions:
Why don't I have cache showing?
What is that huge amount (362M) of "inactive" memory in my top display?
(It varies from a little to alot)
Are "inactive" and "cache" variations on the same thing?
I had thought "cache" was strictly file system cache, so if I don't
see it, I'm not caching any files? (Yuck if not)
Any help would be appreciated.
Thanks,
Wayne
[First time poster...be gentle]
Chad O Hulbert
>
> Hi,
>
> I have a question about system memory in a Xeon/FreeBSD 3.1 system.
>
> Here's my "top" display:
>
> Mem: 35M Active, 362M Inact, 46M Wired, 8349K Buf, 60M Free
> Swap: 1024M Total, 1024M Free
>
Well, what version of FreeBSD are you running? Version ranging from
2.x.x through 4-CURRENT are running on machines around the world and
things change. Although I don't know when the display was changed, I
will guess the field "Cache" is newer than older because I have it and I
run 3-STABLE.
> What is that huge amount (362M) of "inactive" memory in my top display?
> (It varies from a little to alot)
>
> Are "inactive" and "cache" variations on the same thing?
>
> I had thought "cache" was strictly file system cache, so if I don't
> see it, I'm not caching any files? (Yuck if not)
Read the bountiful documentation right under your nose! A simple
'man top' explains all fields and just about everything else you've
asked.
Chad
--
Chad O Hulbert
c...@email.com
"Speed is subsittute fo accurancy."
Americart
> >
> > I have a question about system memory in a Xeon/FreeBSD 3.1 system.
> >
> > Here's my "top" display:
> >
> > Mem: 35M Active, 362M Inact, 46M Wired, 8349K Buf, 60M Free
> > Swap: 1024M Total, 1024M Free
> >
> > Why don't I have cache showing?
>
> Well, what version of FreeBSD are you running? Version ranging from
> 2.x.x through 4-CURRENT are running on machines around the world and
> things change. Although I don't know when the display was changed, I
> will guess the field "Cache" is newer than older because I have it and I
> run 3-STABLE.
3.1 stable
>
> > What is that huge amount (362M) of "inactive" memory in my top display?
> > (It varies from a little to alot)
> >
> > Are "inactive" and "cache" variations on the same thing?
> >
> > I had thought "cache" was strictly file system cache, so if I don't
> > see it, I'm not caching any files? (Yuck if not)
>
> Read the bountiful documentation right under your nose! A simple
> 'man top' explains all fields and just about everything else you've
> asked.
>
I did read it already of course:
Inact: number of pages inactive
Wired: number of pages wired down, including cached file
data pages
Cache: number of pages used for VM-level disk caching
Buf: number of pages used for BIO-level disk caching
Free: number of pages free
Those field defs didn't really answer my questions. Thanks for your
response though. I thought someone here might have some insight or
opinion beyond the man page.
Thanks,
Wayne
Bill Moran
http://www.freebsd.org/handbook/internals-vm.html
Unfortunately, it doesn't explain what "wired" pages are. I've been trying
to figure that out for a number of weeks.
Definitely, the descriptions in "man top" are sparse!
If you get any more details, please cc me.
Thanks
-Bill
Bob Myers
for other system usage, ie, it's reserved by the
kernel, and is not freed and returned for general use.
Bill Moran <dont.li...@columbus.rr.com> wrote in message
news:qigZ2.737$ZS2....@storm.twcol.com...
Matt Dillon
:Americart <amer...@cartserver.com> wrote:
:>Hi,
:>
:>I have a question about system memory in a Xeon/FreeBSD 3.1 system.
:...
:>
:>My questions:
:>
:>Why don't I have cache showing?
:>
:>What is that huge amount (362M) of "inactive" memory in my top display?
:>(It varies from a little to alot)
:>
:>Are "inactive" and "cache" variations on the same thing?
Yes, you have it exactly right. Normally the VM system depreciates pages
in the following order:
wired->active->inactive->cache->free
But if the VM system is very lightly loaded, it does not bother with
the last few steps. It just leaves the pages in the inactive queue.
Pages in the active, inactive, or cache queues are effectively in the
VM cache, so pages in the inactive queue are virtually the same as
pages in the cache ( see note 1 ). Under a heavier VM load the system
makes the distinction between the two in order to regulate the cleaning
of pages ( syncing to backing store or swap ) and to better ensure
that only truely unused pages ( from the 'cache' ) are reused. Under a
light VM load it isn't necessary to make the distinction so the VM
system doesn't bother.
note (1): Another difference between the inactive queue and the cache
is that VM pages may be mapped into processes while being held on the
inactive queue, but are unmapped from processes when moved to the cache
in order to allow the system to reuse them more readily. In a lightly
environment the system is able to avoid unnecessary page faults by
leaving the pages in the inactive queue mapped.
-Matt
:>I had thought "cache" was strictly file system cache, so if I don't
:>see it, I'm not caching any files? (Yuck if not)
:>
:>Any help would be appreciated.
:>
:>Thanks,
:>Wayne
:>[First time poster...be gentle]
--
Matthew Dillon Engineering, HiWay Technologies, Inc. & BEST Internet
Communications
<dil...@best.net> (Please include original email in any response)
Americart
That's just the background info I needed!
Wayne
> :>
> :>I have a question about system memory in a Xeon/FreeBSD 3.1 system.
> :>