On Wed, Mar 16, 2016 at 09:07:59AM +0000, Dr. David Alan Gilbert wrote: > * David Gibson (da...@gibson.dropbear.id.au) wrote: > > On Tue, Mar 15, 2016 at 12:01:04PM +0000, Dr. David Alan Gilbert wrote: > > > * Alexey Kardashevskiy (a...@ozlabs.ru) wrote: > > > > This allows dynamic allocation for migrating arrays. > > > > > > > > Already existing VMSTATE_VARRAY_UINT32 requires an array to be > > > > pre-allocated, however there are cases when the size is not known in > > > > advance and there is no real need to enforce it. > > > > > > > > This defines another variant of VMSTATE_VARRAY_UINT32 with WMS_ALLOC > > > > flag which tells the receiving side to allocate memory for the array > > > > before receiving the data. > > > > > > > > The first user of it is the "pseries" machine (POWER8) with > > > > dynamic DMA windows which existence and size are totally dynamic. > > > > > > You say totally dynamic, how big do they get out of interest? > > > > They're basically used to map all guest RAM. Typically we'd be > > looking at one 64-bit TCE per 64K guest page, so we'd be looking at > > 1/8192th of RAM size. > > > > Since we can in theory have guests in the 1T+ range, that might start > > getting pretty big, so we probably should look at incremental transfer > > of the TCE tables at some point. > > OK, you probably need to bump up MAX_VM_CMD_PACKAGED_SIZE (sysemu.h) > which is an arbitrary size limit for postcopies device data; it's currently > 16MB. It's just there to stop anything silly, so just turn it up a bit. > > However, if it is fixed at one 64-bit TCE per guest page, why do you > need to dynamically allocate it during migration load, can't you > statically allocate once you know guests memory size?
So, guest memory size is what it will be in practice (with Linux
guests), but that's under the guest's control, not ours; at least in
theory it can be different.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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