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List: aix-l
Subject: Re: how much realmem is actually needed?
From: "Santimore, Matthew" <MSantimo () DMC ! ORG>
Date: 2000-05-30 15:13:50
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Take a look at vmstat
this should tell you how your system is acting as far a memory goes.
for instance pay particular attention to sr (scan rate) pi (pages in) and po
(pages out)
the higher your scan rate the busier your system is looking for pages to
swap out.
the more pages it swaps out in order to free mem for applications the more a
memory shortfall you have.
if it is constantly swapping and cpu is constantly waiting then you may want
to add more mem. then you'll
probably uncover another bottleneck , like diskio.
once again its all relative. if the user is happy then there is no problem.
HTH
Matt
> -----Original Message-----
> From: Robert Miller [SMTP:Rmille1@SMUD.ORG]
> Sent: Tuesday, May 30, 2000 10:06
> To: AIX-L@pucc.Princeton.EDU
> Subject: how much realmem is actually needed?
>
> OK, this may sound like a stupid question, but it's been bugging me for
> awhile, so bear with me, if you will...
>
> I have several boxes that, while running, have '0' real memory available
> (looking at them using 'monitor').
> They do have X amount of 'virtual' (swap, if I remember correctly...)
> Is this necessarily a Bad Thing, will it degrade performance?
>
> I've got 2 ideas on it. Somebody tell me which is right, or if I'm totally
> off base here please :}
>
> 1) Having 0 realmem is a Bad Thing - it causes all processes to swap,
> which
> slows everything down.
> 2) Having 0 realmem is No Problem, since all processes are kept in a
> 'sleeping' state, and usually in 'virtual memory'
> (swapped) until they're actually running - obviously, running out of
> swap is always a Bad Thing.
>
> Anybody have any ideas?
>
> Thanks...
>
> --rm
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<TITLE>RE: how much realmem is actually needed?</TITLE>
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<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">Take a look at vmstat </FONT>
</P>
<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">this should tell you how your system is \
acting as far a memory goes.</FONT> <BR><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">for \
instance pay particular attention to sr (scan rate) pi (pages in) and po (pages \
out)</FONT> <BR><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">the higher your scan rate \
the busier your system is looking for pages to swap out.</FONT> <BR><FONT \
COLOR="#0000FF" SIZE=2 FACE="Arial">the more pages it swaps out in order to free mem \
for applications the more a memory shortfall you have.</FONT> <BR><FONT \
COLOR="#0000FF" SIZE=2 FACE="Arial">if it is constantly swapping and cpu is \
constantly waiting then you may want to add more mem. then you'll</FONT> \
<BR><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">probably uncover another bottleneck , \
like diskio.</FONT> </P>
<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">once again its all relative. if \
the user is happy then there is no problem. </FONT> </P>
<BR>
<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">HTH </FONT>
</P>
<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">Matt</FONT>
</P>
<UL>
<P><FONT SIZE=1 FACE="Arial">-----Original Message-----</FONT>
<BR><B><FONT SIZE=1 FACE="Arial">From: </FONT></B> <FONT SIZE=1 \
FACE="Arial">Robert Miller [SMTP:Rmille1@SMUD.ORG]</FONT> <BR><B><FONT SIZE=1 \
FACE="Arial">Sent: </FONT></B> <FONT SIZE=1 FACE="Arial">Tuesday, May 30, \
2000 10:06</FONT> <BR><B><FONT SIZE=1 \
FACE="Arial">To: </FONT></B> <FONT SIZE=1 \
FACE="Arial">AIX-L@pucc.Princeton.EDU</FONT> <BR><B><FONT SIZE=1 \
FACE="Arial">Subject: </FONT></B> <FONT \
SIZE=1 FACE="Arial">how much realmem is actually needed?</FONT> </P>
<P><FONT SIZE=2 FACE="Arial">OK, this may sound like a stupid question, but it's been \
bugging me for</FONT> <BR><FONT SIZE=2 FACE="Arial">awhile, so bear with me, if you \
will...</FONT> </P>
<P><FONT SIZE=2 FACE="Arial">I have several boxes that, while running, have '0' real \
memory available</FONT> <BR><FONT SIZE=2 FACE="Arial">(looking at them using \
'monitor').</FONT> <BR><FONT SIZE=2 FACE="Arial">They do have X amount of 'virtual' \
(swap, if I remember correctly...)</FONT> <BR><FONT SIZE=2 FACE="Arial">Is this \
necessarily a Bad Thing, will it degrade performance?</FONT> </P>
<P><FONT SIZE=2 FACE="Arial">I've got 2 ideas on it. Somebody tell me which is right, \
or if I'm totally</FONT> <BR><FONT SIZE=2 FACE="Arial">off base here please :}</FONT>
</P>
<P><FONT SIZE=2 FACE="Arial">1) Having 0 realmem is a Bad Thing - it causes all \
processes to swap, which</FONT> <BR><FONT SIZE=2 FACE="Arial">slows everything \
down.</FONT> <BR><FONT SIZE=2 FACE="Arial">2) Having 0 realmem is No Problem, \
since all processes are kept in a</FONT> <BR><FONT SIZE=2 FACE="Arial">'sleeping' \
state, and usually in 'virtual memory'</FONT> <BR><FONT SIZE=2 \
FACE="Arial"> (swapped) until they're actually running - obviously, \
running out of</FONT> <BR><FONT SIZE=2 FACE="Arial">swap is always a Bad \
Thing.</FONT> </P>
<P><FONT SIZE=2 FACE="Arial">Anybody have any ideas?</FONT>
</P>
<P><FONT SIZE=2 FACE="Arial">Thanks...</FONT>
</P>
<P><FONT SIZE=2 FACE="Arial">--rm</FONT>
</P>
</UL>
</BODY>
</HTML>
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