Re: [Xen-devel] [PATCH] balloon: selfballooning and post memory info via xenbus,

[Torben Viets <viets@xxxxxxx>]

Dan Magenheimer wrote:
> (Your reply came to me but not to the list... not sure why.
> So I've attached your full reply below.)
>   
thanks, hope this time it works....
>   
> > ah ok, that is my failure, I need a bigger swapdisk ;)
> >     
> Yes, definitely.  If you are creating the swapdisk on an ext3
> filesystem, you might try using sparse files.  They won't
> take up much disk space unless/until they get swapped-to.
> There might be some performance ramifications though.
> (My testing has been with swap disk as a logical volume
> so I can't try sparse.)
>
>   
> > Ok, our plan is to have a high availbilty xen farm. Now we're 
> > beginning
> > with 2 Suns X2200, each has 16GB RAM. The idea, why we like to use
> > selfballooning, because of peak traffic on a server, normal a server
> > needs about 256MB, but when it needs more, it shouldn't be a 
> > problem to
> > give it 4GB. The idea is not to overbook the memory, but have the
> > ability to get rid of memory failures because of peaks.
> >     
> Exactly what it is intended for!
>
> I'd be interested in how it works for guests with memory=4096
> and higher.  All of my testing so far has been on a machine with
> only 2GB of physical memory so I can test lots of guests but
> no large guests. 
>   
I'll test it on monday, now I'm going into my weekend ;) but I think, 
that I wasn't able to get more than 2GB RAM allocated, but I will test 
it on monday again.
PS: In my first mail I've attached my whole signatur, I remove it 
because I get enough spam ;)
Thanks
Torben Viets
> Thanks,
> Dan
>
>   
> > -----Original Message-----
> > From: viets@xxxxxxx [mailto:viets@xxxxxxx]
> > Sent: Friday, May 16, 2008 9:49 AM
> > To: dan.magenheimer@xxxxxxxxxx; xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> > Subject: Re: [Xen-devel] [PATCH] balloon: selfballooning and 
> > post memory
> > info via xenbus,
> >
> >
> > Dan Magenheimer wrote:
> >     
> > > > thanks for the patch, I was waiting for this feature.
> > > >         
> > > Thanks very much for the testing and feedback!  Could you
> > > comment on what you plan to use it for?  (Keir hasn't accepted
> > > it yet, so I am looking for user support ;-)
> > >       
> > Ok, our plan is to have a high availbilty xen farm. Now we're 
> > beginning
> > with 2 Suns X2200, each has 16GB RAM. The idea, why we like to use
> > selfballooning, because of peak traffic on a server, normal a server
> > needs about 256MB, but when it needs more, it shouldn't be a 
> > problem to
> > give it 4GB. The idea is not to overbook the memory, but have the
> > ability to get rid of memory failures because of peaks.
> >
> >     
> > > First question: Do you have a swap (virtual) disk configured and,
> > > if so, how big is it?  (Use "swapon -s" and the size shows in KB.)
> > > Selfballooning shouldn't be run in a domain with no swap disk.
> > > Also, how big is your "memory=" in your vm.cfg file?
> > >       
> > #kernel = "/boot/xen-3.2.0/vmlinuz-2.6.18.8-xenU"
> > #kernel = "/boot/vmlinuz-2.6.18.8-xenU"
> > kernel = "/boot/vmlinuz-selfballooning"
> > memory = 256
> > maxmem = 8192
> > vcpu = 4
> > name = "test.work.de"
> > vif = [ 'bridge=xenvlan323' ]
> > disk = [ 'phy:/dev/sda,hda,w', 'file:/var/swap.img,hdb,w' ]
> > root = "/dev/hda ro"
> > extra = 'xencons=tty'
> >
> >
> >
> > swap_size = 256M
> >
> >     
> > > I'm not able to reproduce your dd failure at all, even with
> > > bs=2047M (dd doesn't permit larger values for bs).
> > > Your program (I called it "mallocmem") does eventually fail for
> > > me but not until i==88.  However, I have a 2GB swap disk configured.
> > >       
> > ah ok, that is my failure, I need a bigger swapdisk ;)
> >     
> > > I think both tests are really measuring the total virtual memory
> > > space configured, e.g. the sum of physical memory (minus kernel
> > > overhead) and configured swap space.  I think you will find that
> > > both will fail similarly with ballooning off and even on a physical
> > > system, just at different points in virtual memory usage.
> > > Indeed, by adding additional output to mallocmem, I can see that
> > > it fails exactly when it attempts to malloc memory larger than
> > > the CommitLimit value in /proc/meminfo.  I expect the same is
> > > true for the dd test.
> > >
> > > Note that CommitLimit DOES go down when memory is ballooned-out
> > > from a guest.  So your test does point out to me that I should
> > > include a warning in the documentation not only that a swap disk
> > > should be configured, but also that the swap disk should be
> > > configured larger for a guest if selfballooning will be turned on.
> > >
> > > Thanks,
> > > Dan
> > >
> > >       
> > > > -----Original Message-----
> > > > From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> > > > [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx]On Behalf Of
> > > > viets@xxxxxxx
> > > > Sent: Friday, May 16, 2008 3:36 AM
> > > > To: xen-devel@xxxxxxxxxxxxxxxxxxx
> > > > Subject: RE: [Xen-devel] [PATCH] balloon: selfballooning and
> > > > post memory
> > > > info via xenbus,
> > > >
> > > >
> > > > Hello,
> > > >
> > > > thanks for the patch, I was waiting for this feature.
> > > >
> > > > I've tried this patch and I've seen that if I malloc a great
> > > > size of memory in time, this fails, but if I malloc a small
> > > > size first and then resize it slowly, it works.
> > > >
> > > > this highly suffisticated (:p) program I use to test the 
> > > >         
> > ballooning:
> >     
> > > > #include <stdio.h>
> > > > #include <unistd.h>
> > > >
> > > > int main () {
> > > >   void *v;
> > > >   int i;
> > > >   for(i=40; i < 50; ++i) {
> > > >     v = malloc((i*32*1024*1024));
> > > >     printf("%i\n", i);
> > > >     if ( v != NULL) {
> > > >       system("cat /proc/xen/balloon");
> > > >       sleep(1);
> > > >       free(v);
> > > >     }
> > > >   }
> > > > }
> > > >
> > > > same effect I've got if I change the blocksize in a dd:
> > > >
> > > > works: dd if=zero of=/test.img count=1 bs=32M
> > > > doesn't work: dd if=zero of=/test.img count=1 bs=256M
> > > >
> > > > Don't know whether this is the right test for this...
> > > >
> > > > greetings
> > > > Torben Viets
> > > >
> > > >
> > > > Dan Magenheimer wrote
> > > >         
> > > > > OK, here's the promised patch.  The overall objective of the
> > > > > patch is to enable limited memory load-balancing capabilities
> > > > > as a step toward allowing limited memory overcommit.  With
> > > > > this and some other minor hackery, I was able to run as
> > > > > many as 15 lightly loaded 512MB domains on a 2GB system
> > > > > (yes, veerrrryyy slooowwwlly).
> > > > >
> > > > > Review/comments appreciated.
> > > > >
> > > > > With this patch, balloon.c communicates (limited) useful
> > > > > memory usage information via xenbus.  It also implements
> > > > > "selfballooning" which applies the memory information
> > > > > locally to immediately adjust the balloon, giving up memory
> > > > > when it is not needed and asking for it back when it is needed,
> > > > > implementing a first-come-first-served system-wide ballooning
> > > > > "policy".  When a domain asks for memory but none is available,
> > > > > it must use its own configured swap disk, resulting in
> > > > > (potentially severe) performance degradation.  Naturally,
> > > > > it is not recommended to turn on selfballooning in a domain
> > > > > that has no swap disk or if performance is more important
> > > > > than increasing the number of VMs runnable on a physical machine.
> > > > >
> > > > > A key assumption is that the Linux variable vm_committed_space
> > > > > is a reasonable first approximation of memory needed by a domain.
> > > > > This approximation will probably improve over time, but is
> > > > > a good start for now.  The variable is bound on the lower end
> > > > > by the recently submitted minimum_target() algorithm patch;
> > > > > thus O-O-M conditions should not occur.
> > > > >
> > > > > The code is a bit complicated in a couple of places because of
> > > > > race conditions involving xenstored startup relative to
> > > > > turning on selfballooning locally.  Because the key variable
> > > > > (vm_committed_space) is not exported by Linux, I implemented
> > > > > a horrible hack which still allows the code to work in a
> > > > > module, however I fully expect that this part of the patch
> > > > > will not be accepted (which will limit the functionality to
> > > > > pvm domains only... probably OK for now).
> > > > >
> > > > > Existing balloon functionality which is unchanged:
> > > > > - Set target for VM from domain0
> > > > > - Set target inside VM by writing to /proc/xen/balloon
> > > > > Existing balloon info on xenbus which is unchanged:
> > > > > - /local/domain/X/memory/target
> > > > > To turn on selfballooning:
> > > > > - Inside a VM: "echo 1 > /proc/xen/balloon"
> > > > > - From domain0: "xenstore-write
> > > > >           
> > > > /local/domain/X/memory/selfballoon 1"
> > > >         
> > > > > To turn off selfballooning:
> > > > > - Inside a VM: "echo 0 > /proc/xen/balloon"
> > > > > - From domain0: "xenstore-write
> > > > >           
> > > > /local/domain/X/memory/selfballoon 0"
> > > >         
> > > > > New balloon info now on xenbus:
> > > > > - /local/domain/X/memory/selfballoon [0 or 1]
> > > > > - /local/domain/X/memory/actual [kB] *
> > > > > - /local/domain/X/memory/minimum [kB] *
> > > > > - /local/domain/X/memory/selftarget [kB] * (only valid if
> > > > >   selfballoon==1)
> > > > >  * writeable only by balloon driver in X when either
> > > > >    selfballooning is first enabled, or target is changed
> > > > >    by domain0
> > > > >
> > > > > Thanks,
> > > > > Dan
> > > > >
> > > > > ===================================
> > > > > Thanks... for the memory
> > > > > I really could use more / My throughput's on the floor
> > > > > The balloon is flat / My swap disk's fat / I've OOM's in store
> > > > > Overcommitted so much
> > > > > (with apologies to the late great Bob Hope)
> > > > >           
> > > > --
> > > >
> > > >
> > > > _______________________________________________
> > > > Xen-devel mailing list
> > > > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > > > http://lists.xensource.com/xen-devel
> > > >
> > > >         
> > >       
> >     
>
> _______________________________________________
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>
>   

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