This led me into an interesting area. I just set a couple of our test servers
to run without swap space. This could put a bigger paging load on VM at times,
but then again simplifying the Linux configuration and having VM do the heavy
lifting are both good selling points. I'm also thinking about when I eventually
hand this work over to someone else. Not having to explain v-disks and the
interplay of paging and swapping between the hypervisor and guests could avoid
confusion and mistakes being made. Of course Linux memory utilization becomes
critical, and we can watch it with something like this and adjust virtual CP
storage accordingly:
ps -eo pmem | awk '{pmem += $1}; END {print "pmem = "pmem"%"}';
Right now our biggest WebSphere server is running comfortably at ~60% memory
used, out of 2G. Is anyone else running swapless servers big or small? If swap
space is considered a safety valve to keep a server up, then I would just as
soon put it on real DASD, and avoid its use with proper memory sizing.
Ray
> -----Original Message-----
> From: Linux on 390 Port [mailto:linux-...@vm.marist.edu] On
> Behalf Of Marcy Cortes
> Sent: Thursday, June 24, 2010 10:34 AM
> To: LINUX-390@VM.MARIST.EDU
> Subject: Re: Memory use question
>
> So with swappiness higher, Linux is making decsions to
> preemptively move something from memory to vdisk. Well, your
> vdisk is in VM's pageable memory too.
> So moving something from one piece of VM memory to another
> piece of VM memory means both parts will have to become
> resident. The source page probably had already been paged
> out by VM if Linux hadn't been using it recently and the
> vdisk page may not have even existed or if it did since it
> had been used before, it was likely paged out too.
>
> Marcy
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