Rik van Riel [off-list ref] writes:

On 7 Jan 2001, Zlatko Calusic wrote:

quoted

Things go berzerk if you have one big process whose working set
is around your physical memory size.

"go berzerk" in what way?  Does the system cause lots of extra
swap IO and does it make the system thrash where 2.2 didn't
even touch the disk ?

Well, I think yes. I'll do some testing on the 2.2 before I can tell
you for sure, but definitely the system is behaving badly where I
think it should not.

quoted

Final effect is that physical memory gets extremely flooded with
the swap cache pages and at the same time the system absorbs
ridiculous amount of the swap space.

This is mostly because Linux 2.4 keeps dirty pages in the
swap cache. Under Linux 2.2 a page would be deleted from the
swap cache when a program writes to it, but in Linux 2.4 it
can stay in the swap cache.

OK, I can buy that.

Oh, and don't forget that pages in the swap cache can also
be resident in the process, so it's not like the swap cache
is "eating into" the process' RSS ;)

So far so good... A little bit weird but not alarming per se.

quoted

For instance on my 192MB configuration, firing up the hogmem
program which allocates let's say 170MB of memory and dirties it
leads to 215MB of swap used.

So that's 170MB of swap space for hogmem and 45MB for
the other things in the system (daemons, X, ...).

Yes, that's it. So it looks like all of my processes are on the
swap. That can't be good. I mean, even Solaris (known to eat swap
space like there's no tomorrow :)) would probably be more polite.

Sounds pretty ok, except maybe for the fact that now
Linux allocates (not uses!) a lot more swap space then
before and some people may need to add some swap space
to their system ...

Yes, I would say really a lot more. Big diffeence.

Also, I don't see a diference between allocated and used swap space on
the Linux. Could you elaborate on that?

Now if 2.4 has worse _performance_ than 2.2 due to one
reason or another, that I'd like to hear about ;)

I'll get back to you later with more data. Time to boot 2.2. :)
-- 
Zlatko
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