Re: [RFC] 0/4 Migration Cache Overview

[Lee Schermerhorn <lee.schermerhorn@hp.com>]

On Tue, 2006-02-21 at 10:04 -0800, Christoph Lameter wrote:
> On Tue, 21 Feb 2006, Marcelo Tosatti wrote:
> 
> > The idea was to create a "partition" inside the swapcache which allows
> > for mapping+offset->pfn translation _without_ actually occupying space
> > in the swap map (an idr table is used instead).
> > 
> > But apparently Christoph's mechanism adds the PFN number into
> > the page table entry itself, thus fulfilling the requirement for
> > "mapping+offset"->pfn indexing required for removal of pages underneath
> > a living process. Is that right?
> 
> Right. Swap ptes contain the index into swap space which I am using to 
> preserve the information contained in the pte's of anonymous pages. Thus 
> the existing swap ptes couild be used. There were just a few minor 
> modifications to the swap functions required.
> 

Are the swap ptes used for migrating pages still reserving swap space on
real swap devices?  I thought this was what the migration cache was
trying to avoid.  Now each running instance of direct migration limits
itself to MIGRATE_CHUNK_SIZE [currently] 256 pages, so if the system has
much swap space at all, this shouldn't place too much of a load on swap
space.  But, it does require that one have SOME swap space to migrate,
right?

Lee

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