Re: [RFC] Remove unswappable anonymous pages off the LRU

[Christoph Lameter <clameter@sgi.com>]

On Thu, 15 Feb 2007, Rik van Riel wrote:

> Christoph Lameter wrote:
> > On Thu, 15 Feb 2007, Rik van Riel wrote:
> > 
> > > Running out of swap is a temporary condition.
> > > You need to have some way for those pages to
> > > make it back onto the LRU list when swap
> > > becomes available.
> > 
> > Yup any ideas how?
> 
> Not really.

Maybe its then best to not move the pages off the LRU when there is some 
swap available. But even if there is no swap available: The user could 
add some later. So there is really no criterion for removing anonymous 
pages off the LRU. We would at least need some list of mlocked pages in 
orderto feed them back to the LRU.
 
> > > For example, we could try to reclaim the swap
> > > space of every page that we scan on the active
> > > list - when swap space starts getting tight.
> > 
> > Good idea.
> 
> I suspect this will be a better approach.  That way
> the least used pages can cycle into swap space, and
> the more used pages can be in RAM.
> 
> The only reason pages are unswappable when we run
> out of swap is that we don't free up the swap space
> used by pages that are in memory.

Well that is another project and not moving pages 
off the LRU.

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