Re: Page host virtual assist patches.

[Nick Piggin <nickpiggin@yahoo.com.au>]

Andrew Morton wrote:
> Martin Schwidefsky <schwidefsky@de.ibm.com> wrote:
> 
>> The basic idea of host virtual assist (hva) is to give a host system
>> which virtualizes the memory of its guest systems on a per page basis
>> usage information for the guest pages. The host can then use this
>> information to optimize the management of guest pages, in particular
>> the paging. This optimizations can be used for unused (free) guest
>> pages, for clean page cache pages, and for clean swap cache pages.
> 
> 
> This is pretty significant stuff.  It sounds like something which needs to
> be worked through with other possible users - UML, Xen, vware, etc.
> 
> How come the reclaim has to be done in the host?  I'd have thought that a
> much simpler approach would be to perform a host->guest upcall saying
> either "try to free up this many pages" or "free this page" or "free this
> vector of pages"?

Definitely. The current patches seem like just an extra layer to do
everything we can already -- reclaim unused pages and populate them
again when they get touched.

And complex they are. Having the core VM have to know about all this
weird stuff seems... not good.

-- 
SUSE Labs, Novell Inc.
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