Re: [Xen-devel] [PATCH V3] X86/vMCE: handle broken page with regard to migration

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 21/11/12 11:07, Ian Campbell wrote:
> On Tue, 2012-11-20 at 18:54 +0000, Liu, Jinsong wrote:
> > Well, let me elaborate more my thought about broken page occur at last iter:
> >
> > Theoretically we can separate 'broken page at last iter' into several 
> > sub-cases, and optimize case by case:
> > 1. if the page (which will break at last iter) is not on dirty bitmap (of last 
> > iter) --> do nothing is OK, target will happily run w/o broken page;
> > 2. if the page (which will break at last iter) is on dirty bitmap (of last iter)
> >    2.1 if at last iter, vmce occur after page copy --> do nothing is OK, target 
> > happily run w/o broken page;
> >    2.2 if vmce occur beofre pfn_type transfer --> do nothing is OK, V2 patch 
> > has correctly handle the case, target will set p2m broken correctly;
> >    2.3 if vmce occur after pfn_type transfer and before copy page to target --> 
> > we need handle this case;
> >
> > Practically considering it's rare enough, and code complication, we handle it 
> > in a simple way (not so optimized but enough for real life):
> > - we don't distinguish if the page is in dirty bitmap of last iter;
> > - we don't prefer adding new hypercall for this corner case, instead we'd like 
> > to re-use currently existed hypercall;
> > - if vmce occur at last iter, we do 1~2 more iter.
> Can't a page break on each "last" iter. i.e. you might actually go
> around as many times as there are pages in the last batch?
I think it would be only if the pages break one by one, at just the 
right time -- that seems pretty unlikely. :-)
 -George

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