On 13.04.14 04:27, Liu ping fan wrote:
On Fri, Apr 11, 2014 at 10:03 PM, Alexander Graf <agraf@xxxxxxx> wrote:
On 11.04.2014, at 13:45, Liu Ping Fan <pingfank@xxxxxxxxxxxxxxxxxx> wrote:
When we mark pte with _PAGE_NUMA we already call mmu_notifier_invalidate_range_start
and mmu_notifier_invalidate_range_end, which will mark existing guest hpte
entry as HPTE_V_ABSENT. Now we need to do that when we are inserting new
guest hpte entries.
What happens when we don't? Why do we need the check? Why isn't it done implicitly? What happens when we treat a NUMA marked page as non-present? Why does it work out for us?
Assume you have no idea what PAGE_NUMA is, but try to figure out what this patch does and whether you need to cherry-pick it into your downstream kernel. The description as is still is not very helpful for that. It doesn't even explain what really changes with this patch applied.
Yeah. what about appending the following description? Can it make
the context clear?
"Guest should not setup a hpte for the page whose pte is marked with
_PAGE_NUMA, so on the host, the numa-fault mechanism can take effect
to check whether the page is placed correctly or not."
Try to come up with a text that answers the following questions in order:
- What does _PAGE_NUMA mean?
- How does page migration with _PAGE_NUMA work?
-> Why should we not map pages when _PAGE_NUMA is set?
- Which part of what needs to be done did the previous _PAGE_NUMA
patch address?
- What's the situation without this patch?
- Which scenario does this patch fix?
Once you have a text that answers those, you should have a good patch
description :).
Alex
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