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Re: [Xen-devel] Ballooning up

To: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Subject: Re: [Xen-devel] Ballooning up
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Tue, 07 Sep 2010 23:26:04 +1000
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 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.


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