I was hoping that someone else would pick up the 1GB PoD task. :P I can try to
implement this feature if deemed necessary.
-Wei
-----Original Message-----
From: Tim Deegan [mailto:Tim.Deegan@xxxxxxxxxx]
Sent: Tuesday, February 23, 2010 4:07 AM
To: Huang2, Wei
Cc: 'xen-devel@xxxxxxxxxxxxxxxxxxx'; Keir Fraser; Xu, Dongxiao
Subject: Re: [Xen-devel] [PATCH][3/4] Enable 1GB for Xen HVM host page
At 17:18 +0000 on 22 Feb (1266859128), Wei Huang wrote:
> This patch changes P2M code to works with 1GB page now.
>
> Signed-off-by: Wei Huang <wei.huang2@xxxxxxx>
> Acked-by: Dongxiao Xu <dongxiao.xu@xxxxxxxxx>
> @@ -1064,6 +1093,19 @@
> if ( unlikely(d->is_dying) )
> goto out_fail;
>
> + /* Because PoD does not have cache list for 1GB pages, it has to remap
> + * 1GB region to 2MB chunks for a retry. */
> + if ( order == 18 )
> + {
> + gfn_aligned = (gfn >> order) << order;
> + for( i = 0; i < (1 << order); i += (1 << 9) )
> + set_p2m_entry(d, gfn_aligned + i, _mfn(POPULATE_ON_DEMAND_MFN),
> 9,
> + p2m_populate_on_demand);
I think you only need one set_p2m_entry call here - it will split the
1GB entry without needing another 511 calls.
Was the decision not to implement populate-on-demand for 1GB pages based
on not thinking it's a good idea or not wanting to do the work? :)
How much performance do PoD guests lose by not having it?
> + audit_p2m(d);
> + p2m_unlock(p2md);
> + return 0;
> + }
> +
> /* If we're low, start a sweep */
> if ( order == 9 && page_list_empty(&p2md->pod.super) )
> p2m_pod_emergency_sweep_super(d);
> @@ -1196,6 +1238,7 @@
> l1_pgentry_t *p2m_entry;
> l1_pgentry_t entry_content;
> l2_pgentry_t l2e_content;
> + l3_pgentry_t l3e_content;
> int rv=0;
>
> if ( tb_init_done )
> @@ -1222,18 +1265,44 @@
> goto out;
> #endif
> /*
> + * Try to allocate 1GB page table if this feature is supported.
> + *
> * When using PAE Xen, we only allow 33 bits of pseudo-physical
> * address in translated guests (i.e. 8 GBytes). This restriction
> * comes from wanting to map the P2M table into the 16MB RO_MPT hole
> * in Xen's address space for translated PV guests.
> * When using AMD's NPT on PAE Xen, we are restricted to 4GB.
> */
Please move this comment closer to the code it describes.
Also maybe a BUG_ON(CONFIG_PAGING_LEVELS == 3) in the order-18 case
would be useful, since otherwise it looks like order-18 allocations are
exempt from the restriction.
Actually, I don't see where you enforce that - do you?
Tim.
--
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, XenServer Engineering
Citrix Systems UK Ltd. (Company #02937203, SL9 0BG)
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