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SubjectRe: 2.4.8/2.4.9 VM problems


On Mon, 20 Aug 2001, Marcelo Tosatti wrote:

>
> ~
> On Mon, 20 Aug 2001, Daniel Phillips wrote:
>
> > On August 20, 2001 09:12 pm, Marcelo Tosatti wrote:
> > > On Mon, 20 Aug 2001, Daniel Phillips wrote:
> > > > On August 20, 2001 09:14 pm, Mike Galbraith wrote:
> > > > > We need to get the pages 'actioned' (the only thing that really matters)
> > > > > off of the dirty list so that they are out of the equation.. that I'm
> > > > > sure of.
> > > >
> > > > Well, except when the page is only going to be used once, or not at all (in
> > > > the case of an unused readahead page). Otherwise, no, we don't want to have
> > > > frequently used pages or pages we know nothing about dropping of the inactive
> > > > queue into the bit-bucket. There's more work to do to make that come true.
> > >
> > > Find riel's message with topic "VM tuning" to linux-mm, then take a look
> > > at the 4th aging option.
> > >
> > > That one _should_ be able to make us remove all kinds of "hacks" to do
> > > drop behind, and also it should keep hot/warm active memory _in cache_
> > > for more time.
> >
> > I looked at it yesterday. The problem is, it loses the information about *how*
> > a page is used: pagecache lookup via readahead has different implications than
> > actual usage.

And ah, I forgot something here.

Your statement which says "pagecache lookup via readahead has different
implications than actual usage" is not really correct.

If you only consider "hot" pages as "pages which have been touched",
you're going to (potentially) fuck heavy streaming IO workloads.

> The other thing that looks a little problematic, which Rik also >
> pointed out, is the potential long lag before the inactive page is
> detected. > A lot of IO can take place in this time, filling up the
> active list with pages > that we could have evicted much earlier.
>
> We're using unlazy page activation on -ac so that is not an issue.
>
>
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