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

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Date:	Wed, 9 Mar 2016 06:18:00 +0000
From:	"Li, Liang Z" <liang.z.li@...el.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Roman Kagan <rkagan@...tuozzo.com>
CC:	"Dr. David Alan Gilbert" <dgilbert@...hat.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

> 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.
> 
> Paolo

I have a VM which has 2GB of RAM, when the guest booted, there were about 1.4GB of free pages.
Then I tried to download a large file from the internet with the browser, after the downloading finished,
there were only 72MB of free pages left, as Roman pointed out, there were quite a lot of Cached memory.
Then I tried to compile the QEMU, after the compiling finished, there were about 1.3G free pages.

So even the cache will increase to a large amount, it will be freed if there are some other specific workloads. 
The cache memory is a big issue that should be taken into consideration.
 How about reclaim some cache before getting the free pages information?  

Liang