[Qemu-devel] Re: [PATCH 15/26] Virtual hash page table handling on pSeries machine'

[Alexander Graf]

On 17.03.2011, at 02:03, David Gibson <address@hidden> wrote:

> On Wed, Mar 16, 2011 at 04:03:47PM +0100, Alexander Graf wrote:
>> On 03/16/2011 05:56 AM, David Gibson wrote:
> [snip]
>>> @@ -248,6 +261,16 @@ static void ppc_spapr_init(ram_addr_t ram_size,
>>>     ram_offset = qemu_ram_alloc(NULL, "ppc_spapr.ram", ram_size);
>>>     cpu_register_physical_memory(0, ram_size, ram_offset);
>>> 
>>> +    /* allocate hash page table */
>>> +    htab_size = 1ULL<<  (pteg_shift + 7);
>> 
>> Linux makes the htab size depend on the provided amount of ram.
>> Shouldn't we do the same?
> 
> Well... maybe.  In fact the guidelines for hash allocation tend to be
> rather larger than really necessary for a Linux guest, so generally
> 16mb for the hash will be fine.  This does also correspond to the
> allocation for the guest hash we use in our experimental kvm code
> (making the hash exactly one hugepage makes the necessary contiguous
> allocation easier).

Hrm - ok :).

Alex