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xen-ia64-devel
Re: [Xen-ia64-devel] Virtual mem map
Le Vendredi 06 Janvier 2006 22:40, Magenheimer, Dan (HP Labs Fort Collins) a
écrit :
> > I am currently thinking about virtual mem map.
> > In Linux, the virtual mem map is (surprise) virtually mapped.
> > In Xen, we can use the same approach or we can manually cut
> > the mem map into
> > several pieces using a mechanism similar to paging.
[...]
> I think you will need to explain a little bit more what you
> mean by "a mechanism similar to paging" before it will
> be possible to comment. Paging, to me, means there is some
> kind of swap drive or backing store to allow more "virtual"
> pages than "physical" pages.
[I have just describe it in my previous mail].
> I spent a lot of time recently digging through the physical
> memory management code of Linux/ia64. It is very messy because
> it has to support a wide variety of physical memory layouts.
> And it makes surprising choices that throw away huge chunks of
> physical memory (anything that doesn't fit conveniently in
> a "granule").
Yes, this is very surprising. At least 16MB of memory are lost! Maybe Xen
can use this memory for itself ?
> Getting this all working on multiple machines
> will probably be a big challenge. It might be best to use
> Linux code that is known to work on many machines.
Sure.
On the other side, Xen (almost) don't use ptc/itc for itself.
> I agree with your concern though that taking TLB misses when
> looking up a page struct in Xen is likely to cause performance
> problems and some difficult bugs. It might be worthwhile to
> put some counters in to see how frequently the memmap is
> accessed and code some defensive bounds checks to ensure
> wild accesses are immediately flagged with a BUG rather than
> resulting in random memory accesses.
I agree.
Tristan.
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- [Xen-ia64-devel] Virtual mem map, Tristan Gingold
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- RE: [Xen-ia64-devel] Virtual mem map, Tian, Kevin
- RE: [Xen-ia64-devel] Virtual mem map, Tian, Kevin
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- RE: [Xen-ia64-devel] Virtual mem map, Tian, Kevin
- RE: [Xen-ia64-devel] Virtual mem map, Magenheimer, Dan (HP Labs Fort Collins)
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