Messages in this thread | | | Subject | Re: Subtle MM bug | From | Zlatko Calusic <> | Date | 07 Jan 2001 23:33:08 +0100 |
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Rik van Riel <riel@conectiva.com.br> writes:
> On 7 Jan 2001, Zlatko Calusic wrote: > > > 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.
> > 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.
> > 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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/
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