Re: [Qemu-devel] [PATCH v3 0/7] Runtime pagesize computation

[Richard Henderson]

On 10/11/2016 03:18 PM, Peter Maydell wrote:
> On 11 October 2016 at 12:20, Richard Henderson <address@hidden> wrote:
> > On 10/11/2016 12:08 PM, Peter Maydell wrote:
> > > I would ideally have liked to finalize things much later, but
> > > this is in practice hugely difficult because so many things
> > > (in particular all the address space/memory system code)
> > > assume the target page size is known.
>
> > Unfortunate.  I suppose that 4k is still better than 1k, but
> > I was hoping to get 16k or 64k (or higher) when the OS is
> > configured to use such.  I.e. totally dynamically configurable
> > upon write to the appropriate cpu register.
>
> I think that would run into problems with migration:
> the migration stream all works in guest-pages of ram and
> a mismatch means migration doesn't work.

Perhaps migration should use definitions based off of TARGET_PAGE_BITS_MIN? 
Dunno how big of a job that would be...

> The trouble is that all the data structures work in terms
> of page sizes (even though we support sub-page allocations
> those are still done by carving up a page-size chunk).
> It could probably be done but it looked like a gargantuan
> task so I decided this was a better compromise.

Fair enough.  This is still an improvement for an interesting guest.


r~