linux-kernel - Re: KVM: memory ballooning bug?

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Message-ID: <20151227234910.GA26512@bbox>
Date:	Mon, 28 Dec 2015 08:49:10 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Konstantin Khlebnikov <koct9i@...il.com>
CC:	Rafael Aquini <aquini@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: KVM: memory ballooning bug?

On Sun, Dec 27, 2015 at 08:23:03PM +0300, Konstantin Khlebnikov wrote:
> On Wed, Dec 23, 2015 at 8:22 AM, Minchan Kim <minchan@...nel.org> wrote:
> > During my compaction-related stuff, I encountered some problems with
> > ballooning.
> >
> > Firstly, with repeated inflating and deflating cycle, guest memory(ie,
> > cat /proc/meminfo | grep MemTotal) decreased and couldn't recover.
> >
> > When I review source code, balloon_lock should cover release_pages_balloon.
> > Otherwise, struct virtio_balloon fields could be overwritten by race
> > of fill_balloon(e,g, vb->*pfns could be critical).
> 
> I guess, in original design fill and leak could be called only from single
> kernel thread which manages balloon. Seems like lock was added
> only for migration. So, locking scheme should be revisited for sure.
> Probably it's been broken by some of recent changes.

When I read git log, it seems to be broken from introdcuing
balloon_compaction.
Anyway, ballooning is out of my interest. I just wanted to go ahead
my test for a long time without any problem. ;-)
If you guys want to redesign the locking scheme fully, please do.
Until that, I can go with my test with my patches I just sent.

Thanks.

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