Re: [PATCH] modified segq for 2.5

[Andrew Morton <akpm@digeo.com>]

Rik van Riel wrote:
> 
> On Mon, 9 Sep 2002, Andrew Morton wrote:
> > Rik van Riel wrote:
> > > On Mon, 9 Sep 2002, Andrew Morton wrote:
> > >
> > > > I fiddled with it a bit:  did you forget to move the write(2) pages
> > > > to the inactive list?  I changed it to do that at IO completion.
> > > > It had little effect.  Probably should be looking at the page state
> > > > before doing that.
> > >
> > > Hmmm indeed, I forgot this.  Note that IO completion state is
> > > too late, since then you'll have already pushed other pages
> > > out to the inactive list...
> >
> > OK.  So how would you like to handle those pages?
> 
> Move them to the inactive list the moment we're done writing
> them, that is, the moment we move on to the next page. We
> wouldn't want to move the last page from /var/log/messages to
> the inactive list all the time ;)

That's easy.

> > > > The inactive list was smaller with this patch.  Around 10%
> > > > of allocatable memory usually.
> > >
> > > It should be a bit bigger than this, I think.  If it isn't
> > > something may be going wrong ;)
> >
> > Well the working set _was_ large.  Sure, we'll be running refill_inactive
> > a lot.  But spending some CPU in there with this sort of workload is the
> > right thing to do, if it ends up in better replacement decisions.  So
> > it doesn't seem to be a problem per-se?
> 
> OK, in that case there's no problem.  If the working set
> really does take 90% of RAM that's a good thing to know ;)

The working set appears to be 100.000% of RAM, hence the wild
swings in throughput when you give or take half a meg.
 
> > Generally, where do you want to go with this code?
> 
> If this code turns out to be more predictable and better
> or equal performance to use-once, I'd like to see it in
> the kernel.  Use-once seems just too hard to tune right
> for all workloads.
> 

gack.  How do we judge that, without waiting a month and
measuring the complaint level?  (Here I go again).
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