Swap with 16 Gb of RAM

Vsevolod Ilyushchenko simonf at cshl.org
Tue Aug 21 11:00:01 CDT 2001


Dirk,

Thank you for you comments. I have abandoned Redhat kernel almost at once -
the server was simply crashing. :) My "SwapCached" entry shows a tad over 2
Gb, so things are not good there either.

Currently I have 2.4.8. Looks like I just need to try 2.4.9 and see what
happens there.

Simon

Dirk Wetter wrote:
> 
> Hi Vsevolod,
> 
> you should definitely go that far ;-)
> 
> I don't know what kernel are you running, but for your purposes
> I wouldn't stick to the ones you're getting from RedHat, Debian, SuSE,
> whatever.
> 
> I am running a constantly growing cluster of 4GB SMP machines, and
> dealing with VM issues under 2.4.x was a painful experience so far.
> I am running 2.4.8pre4, newer kernels haven't been tested
> yet in our enviroment, to 2.4.8 some things changed again in the VM,
> 2.4.9 is not a big step concerning the memory architecture.
> 
> The issue which you have sounds familiar to me: I had kswapd eating
> all my CPU time, and it looked like the machine is heavily swapping, that was
> as of 2.4.6 or .5. However, the machine didn't swap, it only looked like
> it was. kswapd was trying to free pages, and it did it in every
> memory zone. finally i got in touch with one of the VM guys, and
> he came up with a patch, which solved our problem and was
> later integrated into the stock kernel (2.4.7 i think).
> So if you have 16GB of RAM and the early ineffective page scanner tries
> to free pages (also in wrong zones, where there either is no shortage,
> or it might not even help you), it takes a lot of time, 16GB by 4kB
> are 4mio pages which have to be scanned.
>  Also, 2.4.x kernels mark pages still as swapped, also if they are
> in memory again (cached swapping). has the advantage, that if there's
> a memory shortage, the page can be faster swapped out. So the numbers
> for swap which you see might not be the right ones.  Recent kernels
> however have in /proc/meminfo an entry "SwapCached" which gives you
> more insight.
> 
> hope that helped a little bit,
> 
>         ~dirkw
> 
> __________________________________
>  Dirk Wetter @ Renaissance Techn.
>  mailto:<dirkw at rentec dot com>
> 
>  Tue, 21 Aug 2001, Vsevolod Ilyushchenko wrote:
> 
> > Hi,
> >
> > I have a Dell 8450 with 16 Gb of RAM used for running biological
> > computations. Currently I have 3.5 Gb of swap, and sometimes it is almost
> > completely used up even when only 4 Gb of RAM is used. Worse of all,
> > sometimes kswapd takes up a lot of CPU time. Here is a recent free output:
> >
> >              total       used       free     shared    buffers     cached
> > Mem:      16490952   16486332       4620          0        420   12197416
> > -/+ buffers/cache:    4288496   12202456
> > Swap:      3578664    2915448     663216
> >
> > I am trying to understand what is going on, but I do not know much about
> > swap usage or how to debug it. I do not even know about the proper
> > newsgroup/mailing list to ask this question, except the linux-kernel list.
> > (I am not sure whether I should go that far. :)
> >
> > Thanks in advance for any ideas,
> > Simon
> > --
> >  _________
> > |       x |   Simon (Vsevolod ILyushchenko)   simonf at cshl.org
> > | y = e   |
> > |_________|   http://www.simonf.com          simonf at simonf.com
> >
> >               Disclaimer: This is not me.
> >       This is just my mailer talking to your mailer...
> > _______________________________________________
> > Linux-PowerEdge mailing list
> > Linux-PowerEdge at dell.com
> > http://lists.us.dell.com/mailman/listinfo/linux-poweredge
> >
> 
> _______________________________________________
> Linux-PowerEdge mailing list
> Linux-PowerEdge at dell.com
> http://lists.us.dell.com/mailman/listinfo/linux-poweredge

-- 
 _________    
|       x |   Simon (Vsevolod ILyushchenko)   simonf at cshl.org   
| y = e   |                                    
|_________|   http://www.simonf.com          simonf at simonf.com 
                                             
		Disclaimer: This is not me.                    
	This is just my mailer talking to your mailer...



More information about the Linux-PowerEdge mailing list