Re: [Qemu-devel] [PATCH 4/6] pseries: Move hash page table allocation to reset time

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 02/05/2016 01:13 PM, David Gibson wrote:
> At the moment the size of the hash page table (HPT) is fixed based on the
> maximum memory allowed to the guest.  As such, we allocate the table during
> machine construction, and just clear it at reset.
>
> However, we're planning to implement a PAPR extension allowing the hash
> page table to be resized at runtime.  This will mean that on reset we want
> to revert it to the default size.  It also means that when migrating, we
> need to make sure the destination allocates an HPT of size matching the
> host, since the guest could have changed it before the migration.
>
> This patch replaces the spapr_alloc_htab() and spapr_reset_htab() functions
> with a new spapr_reallocate_hpt() function.  This is called at reset and
> inbound migration only, not during machine init any more.


I'd suggest splitting this patch in two (move spapr_hpt_shift_for_ramsize 
to a new patch, or reorganizing it somehow (move 
spapr_hpt_shift_for_ramsize to a different place) - this one is really hard 
to read and make sure that nothing is lost.


> In addition, we add a new helper to compute the recommended hash table size
> for a given RAM size.  We export this as well as spapr_reallocate_hpt(),
> since we'll be needing them elsewhere in future.

Do you already have a patch in your queue to exploit this?

I was told few times to export stuff when I have to...


-- 
Alexey