Re: Why active list and inactive list?

[Balbir Singh]

Nick Piggin wrote:
> 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)
>
> I actually had patches to do "split active lists" a while back.
>
> They worked by lazily moving the page at reclaim-time, based on
> whether or not it is mapped. This isn't too much worse than the
> kernel's current idea of what a mapped page is.
>
> They actually got a noticable speedup of the swapping kbuild
> workload, but at this stage there were some more basic
> improvements needed, so the difference could be smaller today.
>
> The other nice thing about it was that it didn't have a hard
> cutoff that the current reclaim_mapped toggle does -- you could
> opt to scan the mapped list at a lower ratio than the unmapped
> one. Of course, it also has some downsides too, and would
> require retuning...

Thanks, I am motivated to experiment with the idea. I guess I need
to (re)discover the downsides for myself :-)

--
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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