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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

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?

Ian.


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