From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1GShhp-0001ZD-VD for qemu-devel@nongnu.org; Wed, 27 Sep 2006 18:16:41 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1GShhm-0001V1-EG for qemu-devel@nongnu.org; Wed, 27 Sep 2006 18:16:40 -0400 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1GShhm-0001UZ-7V for qemu-devel@nongnu.org; Wed, 27 Sep 2006 18:16:38 -0400 Received: from [66.249.92.168] (helo=ug-out-1314.google.com) by monty-python.gnu.org with esmtp (Exim 4.52) id 1GShmi-0007Qi-SQ for qemu-devel@nongnu.org; Wed, 27 Sep 2006 18:21:45 -0400 Received: by ug-out-1314.google.com with SMTP id j40so98462ugd for ; Wed, 27 Sep 2006 15:16:37 -0700 (PDT) In-Reply-To: <3210330950.20060927165724@planetolsen.com> References: <1ACF2542-5DEE-49B5-8177-5B958911B0F6@gmail.com> <3210330950.20060927165724@planetolsen.com> Mime-Version: 1.0 (Apple Message framework v752.2) Content-Type: multipart/alternative; boundary=Apple-Mail-5-699566215 Message-Id: From: The MoonSeeker Subject: Re: [Qemu-devel] RAM overcomittment Date: Thu, 28 Sep 2006 00:16:32 +0200 Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: James Olsen , qemu-devel@nongnu.org --Apple-Mail-5-699566215 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=ISO-8859-1; delsp=yes; format=flowed Le 27 sept. 06 =E0 23:57, James Olsen a =E9crit : > It seems to me that no change to QEMU is needed for this; it should > already be supported by your host OS. Simply allocate the memory that > you want (256mb, for example) for each virtual machine. Depending on > how many virtual machines you have open at once, as well as the memory > used by the host OS and any other applications you're running, the > host OS will fit the as much as it can in the physical ram, and > automatically swap out the excess allocated memory to disk. > > However, swapping (using virtual memory) will be a huge performance > killer. It will affect the performance of your host OS and all > applications, as well as for your QEMU instances. The problem is the swaping even the VM don't need all of ressource =20 assigned... We lost RAM... By example you run 4 VM who have 256 MB (assigned with -M option) but =20= just use 56MB in most of time.. with qemu we lost 4 X (256-56MB) =3D 800MB of RAM! Somme other virtualization solution like OpenVz and VServer let this =20 RAM overcommitment. On a VM when you make the command free you can =20 show all RAM installed on the workstation, and with file =20 configuration you set the guaranteed RAM (in this case 56MB) and the =20 limite (in this case 256MB). The limit can be reach only for a cup of =20= time (when VM need ressource..)!!! Do you understant what I mean? I'd like to create an open network simulator based on qemu but this =20 restriction can't let me use qemu... What do you think? =20= --Apple-Mail-5-699566215 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=ISO-8859-1
Le 27 sept. 06 =E0 = 23:57, James Olsen a =E9crit :

It seems to me that no = change to QEMU is needed for this; it should

already be supported by your = host OS. Simply allocate the memory that

you want (256mb, for example) for each = virtual machine. Depending on

how many virtual machines you have open at once, as well as = the memory

used by = the host OS and any other applications you're running, the

host OS will fit the as much = as it can in the physical ram, and

automatically swap out the excess allocated memory to = disk.


However, swapping (using virtual memory) will be a = huge performance

killer. It will affect the performance of your host OS and = all

applications, as well as for your QEMU instances.

=

The problem is the swaping even the VM don't = need all of ressource assigned... We lost RAM...

By example you run 4 VM who = have 256 MB (assigned with -M option) but just use 56MB in most of = time..=A0

with = qemu we lost 4 X (256-56MB) =3D 800MB of RAM!

Somme other virtualization = solution like OpenVz and VServer let this RAM overcommitment. On a VM = when you make the command free you can show all RAM installed on the = workstation, and with file configuration you set the guaranteed RAM (in = this case 56MB) and the limite (in this case 256MB). The limit can be = reach only for a cup of time (when VM need ressource..)!!!

Do you understant what I = mean?

I'd = like to create an open network simulator based on qemu but this = restriction can't let me use qemu...

What do you = think?=A0


=A0
= --Apple-Mail-5-699566215--