linux-kernel - Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization

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Message-ID: <20160304185120.GB2588@work-vm>
Date:	Fri, 4 Mar 2016 18:51:21 +0000
From:	"Dr. David Alan Gilbert" <dgilbert@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	"Li, Liang Z" <liang.z.li@...el.com>,
	Roman Kagan <rkagan@...tuozzo.com>,
	"ehabkost@...hat.com" <ehabkost@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"mst@...hat.com" <mst@...hat.com>,
	"quintela@...hat.com" <quintela@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"amit.shah@...hat.com" <amit.shah@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"rth@...ddle.net" <rth@...ddle.net>
Subject: Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration
 optimization

* Paolo Bonzini (pbonzini@...hat.com) wrote:
> 
> 
> On 04/03/2016 15:26, Li, Liang Z wrote:
> >> > 
> >> > The memory usage will keep increasing due to ever growing caches, etc, so
> >> > you'll be left with very little free memory fairly soon.
> >> > 
> > I don't think so.
> > 
> 
> Roman is right.  For example, here I am looking at a 64 GB (physical)
> machine which was booted about 30 minutes ago, and which is running
> disk-heavy workloads (installing VMs).
> 
> Since I have started writing this email (2 minutes?), the amount of free
> memory has already gone down from 37 GB to 33 GB.  I expect that by the
> time I have finished running the workload, in two hours, it will not
> have any free memory.

But what about a VM sitting idle, or that just has more RAM assigned to it
than is currently using.
 I've got a host here that's been up for 46 days and has been doing some
heavy VM debugging a few days ago, but today:

# free -m
              total        used        free      shared  buff/cache   available
Mem:          96536        1146       44834         184       50555       94735

I very rarely use all it's RAM, so it's got a big chunk of free RAM, and yes
it's got a big chunk of cache as well.

Dave

> 
> Paolo
--
Dr. David Alan Gilbert / dgilbert@...hat.com / Manchester, UK