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

From: Richard Henderson
Subject: Re: [Qemu-arm] [PATCH v3 0/7] Runtime pagesize computation
Date: Tue, 11 Oct 2016 20:34:53 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0

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.


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