Re: KVM architecture docs

[Avi Kivity <avi@qumranet.com>]

Javier Guerra wrote:
> On 3/4/08, Avi Kivity <avi@qumranet.com> wrote:
>   
>>  apply to kvm guests.  With mmu notifiers, the trend will grow even stronger.
>>     
>
> could you (or anybody) elaborate on that? the mmu-related threads show
> lots of progress, but it's way (way) out of my league.
>
> AFAICT, it's about the infrastructure to later write drivers (virtio?)
> to DMA-heavy hardware (IB, RDMA, etc).  am i wrong?  or is it
> something more complete (like a ready to use driver)?
>
>   

mmu notifiers provide a way for the core Linux memory management code to 
propagate changes in how Linux views a process' memory map to external 
memory management units that are also interested in that memory map.  
These changes include things like swapping, page migration, changes to 
memory protection, defragmentation, and copy-on-write.  In this context, 
kvm appears as a dma capable memory controller, like RDMA NICs or GPUs.

For kvm, this is important as it allows all those features to be used 
transparently with guests.

- swapping allows you to overcommit memory
- page migration allows optimization of memory placement within the host 
in response to changing workloads
- defragmentation will allow (if/when it is merged into Linux) more 
widespread use of large pages, which improve performance
- copy-on-write allows sharing identical pages of memory among guests, 
increasing guest density

-- 
error compiling committee.c: too many arguments to function


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