Page in/out counts - Good? Bad? Ugly? Other? [Mac Systems]

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From: Don Bruder on 25 Jul 2010 02:58

Nothing critical, just curious -

Got an AGP G4 running 10.4.11 with 960 megs of physical RAM.

$ uptime
23:51 up 44 days, 18:02, 2 users, load averages: 0.76 0.77 0.51

A few seconds later, opening up Activity Monitor and kicking over to the
System Memory pane shows 1027860 page ins, and 73376 page outs.

I haven't been noticing any particular problems or anything like that,
but I got curious and took a look, and now that I've looked, I don't
know if what I'm seeing is good, bad, in between, or "Oh My God!
Emergency Action Needed!"

I've never really seen a good, clear explanation of precisely what the
page-in/out counts mean (nothing I've seen has been much more in-depth
than "it has to do with virtual memory and is related to how much
physical memory you have and how many programs you try to run at the
same time, along with how memory hungry they are") so I'm just plain not
sure what to make of the numbers I'm seeing.

Anyone?

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From: David Empson on 25 Jul 2010 08:20

Don Bruder <dakidd(a)sonic.net> wrote:

> Nothing critical, just curious -
>
> Got an AGP G4 running 10.4.11 with 960 megs of physical RAM.
>
> $ uptime
> 23:51 up 44 days, 18:02, 2 users, load averages: 0.76 0.77 0.51
>
> A few seconds later, opening up Activity Monitor and kicking over to the
> System Memory pane shows 1027860 page ins, and 73376 page outs.
>
> I haven't been noticing any particular problems or anything like that,
> but I got curious and took a look, and now that I've looked, I don't
> know if what I'm seeing is good, bad, in between, or "Oh My God!
> Emergency Action Needed!"
>
> I've never really seen a good, clear explanation of precisely what the
> page-in/out counts mean (nothing I've seen has been much more in-depth
> than "it has to do with virtual memory and is related to how much
> physical memory you have and how many programs you try to run at the
> same time, along with how memory hungry they are") so I'm just plain not
> sure what to make of the numbers I'm seeing.

In my experience:

1. The "Page ins" count goes up all the time as part of normal activity.

As a result, the "Page ins" counter has little or no diagnostic value.

Many files (including applications and data files) are loaded into
memory using a mechanism whereby the file is "mapped" into the virtual
memory space, so the content of that file forms part of the virtual
memory. A "page in" is then used to read information from the file
(virtual memory) into real memory (RAM) when that part of the virtual
memory is accessed.

2. A nonzero value in the "Page outs" count almost always indicates a
situation where your computer needed more real memory (RAM) than is
installed.

It is possible for the same file mapping scheme described above to be
invoked for the purposes of writing information out from real memory to
virtual memory in normal operation of an application, but this is
relatively rare.

The most common reason for a "page out" is that the computer needed more
real memory for something, but none was available. It therefore has to
pick some area of memory which was not recently used, and write it out
to a "swap file" to make room for something else. This causes the "Page
outs" count to increase.

If there is heavy page out activity, it is usually associated with
loading something else into memory, so this tends to result in a lot of
hard drive activity, and the computer goes very slowly. You will not
enjoy the experience as you will be seeing spinning beachballs and
pauses.

The solution is generally to add more real memory to the computer, or to
reduce the amount of memory required, e.g. by not running quite so many
applications all at the same time, or to reduce the memory required by
some of those applications.

The "Page outs" counter in Activity monitor can be a useful tool to
diagnose whether the computer has enough memory for a particular task.
If you have Activity Monitor running and you see the "Page outs" counter
increasing, then at that moment the computer does not have enough memory
for whatever it is doing. If it is increasing rapidly then you may have
a major performance hit.

A static reading in "Page outs" on a system with a high uptime is not
useful in itself, as there is no information about whether that number
appeared in a single rapid burst (one application needed a vast amount
of memory), or in moderate sized bursts each time a particular
application was launched (that application needed a fair amount more
memory than you have), or on occasions when lots of applications were
run at the same time (run fewer applications at once), or it was
trickling over time (which may not even be noticed by the user) due to
having only slightly insufficient memory during certain tasks.

--
David Empson
dempson(a)actrix.gen.nz

From: Bob Harris on 25 Jul 2010 10:17

In article <i2gn7j$115$3(a)news.eternal-september.org>,
Don Bruder <dakidd(a)sonic.net> wrote:

> Nothing critical, just curious -
>
> Got an AGP G4 running 10.4.11 with 960 megs of physical RAM.
>
> $ uptime
> 23:51 up 44 days, 18:02, 2 users, load averages: 0.76 0.77 0.51
>
> A few seconds later, opening up Activity Monitor and kicking over to the
> System Memory pane shows 1027860 page ins, and 73376 page outs.

1027860 pageins in 44 days is 16 pageins per minute
73376 pageouts in 44 days is 1 pageout per minute

Just remember there are lies, damn lies, and statistics.
Averaging the values can put things into perspective.

> I haven't been noticing any particular problems or anything like that,

Then do not worry about it.

> but I got curious and took a look, and now that I've looked, I don't
> know if what I'm seeing is good, bad, in between, or "Oh My God!
> Emergency Action Needed!"
>
> I've never really seen a good, clear explanation of precisely what the
> page-in/out counts mean (nothing I've seen has been much more in-depth
> than "it has to do with virtual memory and is related to how much
> physical memory you have and how many programs you try to run at the
> same time, along with how memory hungry they are") so I'm just plain not
> sure what to make of the numbers I'm seeing.
>
> Anyone?

Others have explained where the pagein/pageout numbers come from.

If you decide you want to see when those events happen, you can
open an Applications -> Utilities -> Terminal session and run

sar -g 60 100

Which will report the number of pageouts once a minute for 100
minutes (change the values to suite your tastes)

Now let this run while you do your normal tasks. You can go back
and look at the output and see where your pageout activity
occurred, and correlate with what you were doing at the time.

Years ago, I had a G4 Mac tower with 640MB. It mostly ran OK, but
I noticed slowness when I switched between applications. Using
the above I noticed that when I switched, there was a burst of
pageout activity as the application I was switching to, was paged
back into memory, and something already in memory was paged out.

I increased the memory to 1.5GB and things were greatly improved.

Bob Harris

From: Kevin McMurtrie on 25 Jul 2010 16:46

From: Don Bruder on 25 Jul 2010 17:46

In article
<nospam.News.Bob-513FC6.10174225072010(a)news.eternal-september.org>,
Bob Harris <nospam.News.Bob(a)remove.Smith-Harris.us> wrote:

> In article <i2gn7j$115$3(a)news.eternal-september.org>,
> Don Bruder <dakidd(a)sonic.net> wrote:
>
> > Nothing critical, just curious -
> >
> > Got an AGP G4 running 10.4.11 with 960 megs of physical RAM.
> >
> > $ uptime
> > 23:51 up 44 days, 18:02, 2 users, load averages: 0.76 0.77 0.51
> >
> > A few seconds later, opening up Activity Monitor and kicking over to the
> > System Memory pane shows 1027860 page ins, and 73376 page outs.
>
> 1027860 pageins in 44 days is 16 pageins per minute
> 73376 pageouts in 44 days is 1 pageout per minute
>
> Just remember there are lies, damn lies, and statistics.
> Averaging the values can put things into perspective.

Heh... Yeah, that too! :)

>
> > I haven't been noticing any particular problems or anything like that,
>
> Then do not worry about it.

I'm nowhere *NEAR* "worried" about it. But when my "curious bump" gets
to itching, you betcha I'm gonna try to scratch it!

>
> > but I got curious and took a look, and now that I've looked, I don't
> > know if what I'm seeing is good, bad, in between, or "Oh My God!
> > Emergency Action Needed!"
> >
> > I've never really seen a good, clear explanation of precisely what the
> > page-in/out counts mean (nothing I've seen has been much more in-depth
> > than "it has to do with virtual memory and is related to how much
> > physical memory you have and how many programs you try to run at the
> > same time, along with how memory hungry they are") so I'm just plain not
> > sure what to make of the numbers I'm seeing.
> >
> > Anyone?
>
> Others have explained where the pagein/pageout numbers come from.

Yep, I see that now that there's been time for responses to be made/get
to my server.

>
> If you decide you want to see when those events happen, you can
> open an Applications -> Utilities -> Terminal session and run
>
> sar -g 60 100
>
> Which will report the number of pageouts once a minute for 100
> minutes (change the values to suite your tastes)

Something to try one of these days.
FWIW, since I posted the original message, page ins have gone to 100518,
while page outs have remained unchanged at 73376. Clearly, I'm paging
"in" a whole helluva bunch more than "out".

Equally clearly (now) it's a "nothing to worry about" concept. I simply
didn't have any idea if I was looking at "be afraid!" or "who cares?"
numbers. It now seems fairly obvious that the numbers I'm seeing fall
pretty solidly into the "unless you're curious, who cares?" category.

> Years ago, I had a G4 Mac tower with 640MB. It mostly ran OK, but
> I noticed slowness when I switched between applications. Using
> the above I noticed that when I switched, there was a burst of
> pageout activity as the application I was switching to, was paged
> back into memory, and something already in memory was paged out.
>
> I increased the memory to 1.5GB and things were greatly improved.
>
> Bob Harris

I don't have much in the way of plans for bumping the RAM in this
particular rig - As of right now, it's my "primary backup" machine -
It's not giving me anything resembling trouble, and besides, it's
*SUPPOSED* to be my secondary rig, but I just haven't had the ambition
to actually pull the pieces out of it and transfer them into the DP MDD
that's nominally my "primary" and is sitting just to my left.

The MDD is maxed out at a full 2GB, and it's waiting for me to
(eventually...) transplant the USB2 card, third-party airport card, and
misc other improvements out of the AGP and be physically moved into
place as "primary". For now, it sits there (relatively) quietly helping
me test my code, and every now and again, opening up a second copy of
Diablo II for "mule work". One of these days...

Speaking of "quietly"... This MDD is one of those afflicted with the
known "extraneous ticks, clicks, buzzes and whirrs" in the sound system
issue - at least, it is when I just plug a set of speakers into the
sound-out jack. Anybody know (before I go to the effort of clearing
space and moving it into range of the USB cable that feeds the DSS-80s
currently plugged into the AGP with less than 2 inches of slack to
spare) if that problem goes away if/when I plug in something like a set
of Microsoft DSS-80 speakers via USB?

--
Email shown is deceased. If you would like to contact me by email, please
post something that makes it obvious in this or another group you see me
posting in with a "how to contact you" address, and I'll get back to you.

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