Xen devel - Jun 2007 - [PATCH] Fix balloon handling of highmem pages

I knocked up a quick patch to fix the balloon driver''s handling of
highmem
pages.  Should apply cleanly to the Linux dev tree.  I can also submit it for 
3.1 if wanted.

Without this, LowTotal can go negative (given it''s an unsigned integer)
and
then appears as ~4Gig, which is a bit silly.

I beliee this fixes Anthony Wright''s bug #733 in Bugzilla 
(http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=733).  Credit to 
Anthony for noticing the problem, and figuring out that he was actually 
seeing an unsigned int going "negative".

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!


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Applied, but have you tested with ''mem='' on the domain cmdline
to give it a
memmap bigger than its original allocation of memory? In this case it looks
like the code in mm/init-xen.c does the right thing in tandem with this
patch (i.e., it increments totalhigh_pages for each not-currently-present
page, and you then decrement again when the not-present pages get added to
the balloon). But I''m not 100% certain and it could do with being
tested.

 Thanks,
 Keir

On 29/6/07 16:53, "Mark Williamson"
<mark.williamson@cl.cam.ac.uk> wrote:
> I knocked up a quick patch to fix the balloon driver''s handling of
highmem
> pages.  Should apply cleanly to the Linux dev tree.  I can also submit it
for
> 3.1 if wanted.
> 
> Without this, LowTotal can go negative (given it''s an unsigned
integer) and
> then appears as ~4Gig, which is a bit silly.
> 
> I beliee this fixes Anthony Wright''s bug #733 in Bugzilla
> (http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=733).  Credit to
> Anthony for noticing the problem, and figuring out that he was actually
> seeing an unsigned int going "negative".
> 
> Cheers,
> Mark


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Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel

> Applied, but have you tested with ''mem='' on the domain
cmdline to give it a
> memmap bigger than its original allocation of memory? In this case it looks
> like the code in mm/init-xen.c does the right thing in tandem with this
> patch (i.e., it increments totalhigh_pages for each not-currently-present
> page, and you then decrement again when the not-present pages get added to
> the balloon). But I''m not 100% certain and it could do with being
tested.
Good point.

I checked through that code, and agreed with your assessment.  Also just 
tested it, my domain booted successfully with mem=4G and was able to expand 
(and shrink again) without exploding or doing anything obviously crazy.

Cheers,
Mark
>  Thanks,
>  Keir
>
> On 29/6/07 16:53, "Mark Williamson"
<mark.williamson@cl.cam.ac.uk> wrote:
> > I knocked up a quick patch to fix the balloon driver''s
handling of
> > highmem pages.  Should apply cleanly to the Linux dev tree.  I can
also
> > submit it for 3.1 if wanted.
> >
> > Without this, LowTotal can go negative (given it''s an
unsigned integer)
> > and then appears as ~4Gig, which is a bit silly.
> >
> > I beliee this fixes Anthony Wright''s bug #733 in Bugzilla
> > (http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=733).  Credit
to
> > Anthony for noticing the problem, and figuring out that he was
actually
> > seeing an unsigned int going "negative".
> >
> > Cheers,
> > Mark


-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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