RE: [Xen-devel] Re: [RFC][PATCH] Basic support for page offline

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

Keir Fraser <mailto:keir.fraser@xxxxxxxxxxxxx> wrote:
> On 13/02/2009 17:03, "Tim Deegan" <Tim.Deegan@xxxxxxxxxx> wrote:
> 
>> I'll leave page_offline_xen.patch to Keir since he's said he'll do it,
>> but 700 new lines of code seems like quite a lot -- surely some subsets
>> of he existing buddy splitting and merging code could be split out and
>> reused?
> 
> It could indeed surely be half the size. It's split for some
> reason into a
> chain of about five functions, each of which does a little bit
> of the work.
> Just merge them all together. And unless you have a good reason for
> currently expecting to offline large ranges of pages, and can measure a
> substantial performance difference, I would actually just
> offline one page a
> at a time -- implement that in a function and call it
> repeatedly from a for
> loop. It will be far less complex and for bad-page offlining
> should perform
> just fine.

The reasonto offline large ranges of pages is to offline a DIMM, but yes that 
may not important currently, also that is not performance critical. We only 
support one page each time, that is sure to be much simpler. 

> 
> Also some comments about what the difference is between
> offlining, offlined,
> and broken would be nice. The change in free_heap_pages() to preserve
> PGC_offlining|PGC_broken struck me as particularly worrying --
> no sane C
> programmer should write it like that, which just makes me more
> worried about
> the verbosity of the rest.

Sure, will add comments for how the page status change.

Thanks
Yunhong Jiang

> 
> -- Keir

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