Re: [Xen-devel] [PATCH 2 of 3] Make p2m lookups fully synchronized wrt modifications

["Andres Lagar-Cavilla" <andres@xxxxxxxxxxxxxxxx>]

> At 08:41 -0800 on 24 Nov (1322124101), Andres Lagar-Cavilla wrote:
>> Here is one solution to consider: do not lock the p2m on lookups in
>> shadow
>> mode. Shadow mode does not support paging out and sharing of pages,
>> which
>> are primary reasons why we want synchronized p2m lookups. The hap cases
>> where there is an inversion of the p2m_lock -> paging_lock order are
>> reasonably simple to handle.
>>
>> The other option is to invert the order and place paging_lock ->
>> p2m_lock,
>> but that will raise another set of potential inversions. I think this is
>> a
>> no go.
>
> Is there scope for having the p2m lock split out into the overall one
> (needed for allocations &c) and the per-record ones, and have them at
> different levels in the lock hierarchy?
I think it's saner to go with one big lock and then shard it if we run
into performance problems. Your proposal, actually :)

Now, I'm thinking of splitting ... the paging lock. It covers way too much
ground right now, and many of these inversions would become more
tractable. Thinking of paging_alloc_lock, paging_logdirty_lock,
paging_lock.

Thanks,
Andres
>
> Tim.
>



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel