Re: [vserver] max physical memory / mixing 32bit / 64bit

From: Thomas Weber <>
Date: Thu 17 Apr 2008 - 22:11:36 BST
Message-Id: <1208466696.852.508.camel@utumno>

Am Donnerstag, den 17.04.2008, 19:24 +0200 schrieb Bruno:
> On Thursday 17 April 2008 19:04:17 Oliver Welter wrote:
> > Hi Folks,
> >
> > I am currently running four small pizzaboxes with 32bit pentiums and
> > 2-4Gig of Ram each which is doing pretty fine.
> >
> > I want to replace those boxes with one bigger box, discussion is on a
> > Dual CPU Xeon Box with 32Gig RAM.
> >
> > 1) Is it possible at all, and if so, what do I loose when I run the old
> > 32bit guests on a 64bit Host?
> >
> > 2) Are there any limits regarding memory consumption of a single guest?
> >
> > regards
> >
> > Oliver
> Hi Oliver,
> Running 32bit guests on 64bit host does not cause any special problem. It's
> the same as running 32bit userspace on 64bit kernel (vserver isolation put
> apart)
> Unless you have memory hog applications running inside the guest (each 32bit
> process being limited to 32bit address space) there is no benefit in
> switching the guests to 64bit. (the guests will even be a little bit less
> memory hungry as most datatypes are 32bit instead of 64bit)
> Just make sure you enable support for 32bit ELF binaries when you compile your
> kernel.
> You can also mix 32bit and 64bit guests on your 64bit host kernel (wether host
> userspace is 32bit, 64bit or multilib=mixture makes no difference)

I can second this, almost.

- I'm running a 32bit ubuntu guest in a vserver for converting videos
(vdr recordings from another diskless box). The same vserver works fine
on a 32bit AMD host whereas it doesn't work 100% on the same host in
64bit mode or on another 64bit opteron server. That means there is
content that it does convert just fine and other stuff that makes
different components barf. Haven't had time to dig deeper into it yet,
though it seems that mplayer/mencoder and java are causing the problems.

- A customer had to tune java inside a 32bit guest on a 64bit host
because of issues with the memory (wrongly) recognized by java inside
the guest. This has been done without me beeing involved, so I can't be
more specific.

Generally it just works though. I'm running plenty of vservers (mostly
still 32, some 64bit) on 64bit hosts just fine. Wouldn't want to run the
hosts on 32bit.

Received on Thu Apr 17 22:12:18 2008

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