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Re: [Xen-devel] Ballooning up

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] Ballooning up
From: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Date: Tue, 7 Sep 2010 15:10:10 +0100
Cc: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "Xen-devel@xxxxxxxxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, Daniel Kiper <dkiper@xxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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On Tue, 2010-09-07 at 14:26 +0100, Jeremy Fitzhardinge wrote:
> On 09/07/2010 08:14 PM, Ian Campbell wrote:
> > On Tue, 2010-09-07 at 09:36 +0100, Jeremy Fitzhardinge wrote:
> >> I finally got around to implementing "ballooning up" in the pvops
> >> kernels.  Now if you start a domain with "memory=X maxmem=Y", the domain
> >> will start with X MB of memory, but you can use "x[ml] mem-set" to
> >> expand the domain up to Y.
> > Cool. What did the issue with plymouth and friends turn out to be?
> >
> It was totalram_pages getting decremented when pages were being appended
> to the balloon, even though those pages were never counted.  So it got
> very low, and while it isn't actually used to account for how much free
> memory there is, some random pieces of code use something based on it to
> get a rough metric for free memory and block waiting for it to go up, or
> EAGAIN (or something).
> It was a bit hard to directly observe because totalram_pages doesn't get
> displayed directly in /proc/meminfo, but removing the decrement showed
> that was the problem.

Subtle! Well spotted.


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