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

[David Gibson]

On Mon, Feb 08, 2016 at 03:44:18PM +1100, Alexey Kardashevskiy wrote:
> 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.

Good idea, I'll do that.

> >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...

True, I'll look at that again.

-- 
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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