Re: Why active list and inactive list?

[Balbir Singh]

Christoph Lameter wrote:
> On Tue, 23 Jan 2007, Balbir Singh wrote:
>
> > This makes me wonder if it makes sense to split up the LRU into page
> > cache LRU and mapped pages LRU. I see two benefits
> >
> > 1. Currently based on swappiness, we might walk an entire list
> >    searching for page cache pages or mapped pages. With these
> >    lists separated, it should get easier and faster to implement
> >    this scheme
> > 2. There is another parallel thread on implementing page cache
> >    limits. If the lists split out, we need not scan the entire
> >    list to find page cache pages to evict them.
> >
> > Of course I might be missing something (some piece of history)
>
> This means page cache = unmapped file backed page right? Otherwise this
> would not work. I always thought that the page cache were all file backed
> pages both mapped and unmapped.

Yes, unfortunately my terminology was not clear. I mean unmapped file
backed pages.

> With the proposed schemd you would have to move pages between lists if
> they are mapped and unmapped by a process. Terminating a process could
> lead to lots of pages moving to the unnmapped list.

When you unmap or map, you need to touch the pte entries and know the
pages involved, so shouldn't be equivalent to a list_del and list_add
for each page impacted by the map/unmap operation?

--
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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