Re: Re: [kvm] Re: Questions about duplicate memory work

From: Avi Kivity <avi@redhat.com>
To: Robin Lee Powell <rlpowell@digitalkingdom.org>
Cc: Emmanuel Noobadmin <centos.admin@gmail.com>,
	kvm@vger.kernel.org, Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: Re: [kvm] Re: Questions about duplicate memory work
Date: Tue, 27 Sep 2011 12:49:29 +0300	[thread overview]
Message-ID: <4E819C29.9040000@redhat.com> (raw)
In-Reply-To: <20110927090000.GC28218@stodi.digitalkingdom.org>

On 09/27/2011 12:00 PM, Robin Lee Powell wrote:
> On Tue, Sep 27, 2011 at 01:48:43AM -0700, Robin Lee Powell wrote:
> >  On Tue, Sep 27, 2011 at 04:41:33PM +0800, Emmanuel Noobadmin wrote:
> >  >  On 9/27/11, Robin Lee Powell<rlpowell@digitalkingdom.org>  wrote:
> >  >  >  On Mon, Sep 26, 2011 at 04:15:37PM +0800, Emmanuel Noobadmin
> >  >  >  wrote:
> >  >  >>  It's unrelated to what you're actually using as the disks,
> >  >  >>  whether file or block devices like LVs. I think it just makes
> >  >  >>  KVM tell the host not to cache I/O done on the storage device.
> >  >  >
> >  >  >  Wait, hold on, I think I had it backwards.
> >  >  >
> >  >  >  It tells the *host* to not cache the device in question, or the
> >  >  >  *VMs* to not cache the device in question?
> >  >
> >  >  I'm fairly certain it tells the qemu not to cache the device in
> >  >  question. If you don't want the guest to cache their i/o, then the
> >  >  guest OS should be configured if it allows that. Although I'm not
> >  >  sure if it's possible to disable disk buffering/caching system
> >  >  wide in Linux.
> >
> >  OK, great, thanks.
> >
> >  Now if I could just figure out how to stop the host from swapping
> >  out much of the VMs' qemu-kvm procs when it has almost a GiB of RAM
> >  left.  -_-  swappiness 0 doesn't seem to help there.
>
> Grrr.
>
> I turned swap off to clear it.  A few minutes ago, this host was at
> zero swap:
>
> top - 01:59:10 up 10 days, 15:17,  3 users,  load average: 6.39, 4.26, 3.24
> Tasks: 151 total,   1 running, 150 sleeping,   0 stopped,   0 zombie
> Cpu(s):  6.6%us,  1.0%sy,  0.0%ni, 85.9%id,  6.3%wa,  0.0%hi,  0.2%si,  0.0%st
> Mem:   8128772k total,  6511116k used,  1617656k free,    14800k buffers
> Swap:  8388604k total,   672828k used,  7715776k free,    97536k cached
>
>    PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
>   2504 qemu      20   0 2425m 1.8g  448 S 10.0 23.4   3547:59 qemu-kvm
>   2258 qemu      20   0 2425m 1.7g  444 S  2.7 21.7   1288:15 qemu-kvm
> 18061 qemu      20   0 2433m 1.8g  428 S  2.3 23.4 401:01.99 qemu-kvm
> 10335 qemu      20   0 1864m 861m  456 S  1.0 10.9   2:04.26 qemu-kvm
> [snip]
>
> Why is it doing this?!?  ;'(
>

Please post the contents of /proc/meminfo and /proc/zoneinfo when this 
is happening.

-- 
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