Re: Subtle MM bug

[Rik van Riel]

On 17 Jan 2001, Zlatko Calusic wrote:
> Rik van Riel <[e-mail]> writes:
>
> > > Second test: kernel compile make -j32 (empirically this puts the
> > > VM under load, but not excessively!)
> > >
> > > 2.2.17 -> make -j32  392.49s user 47.87s system 168% cpu 4:21.13 total
> > > 2.4.0  -> make -j32  389.59s user 31.29s system 182% cpu 3:50.24 total
> > >
> > > Now, is this great news or what, 2.4.0 is definitely faster.
> >
> > One problem is that these tasks may be waiting on kswapd when
> > kswapd might not get scheduled in on time. On the one hand this
> > will mean lower load and less thrashing, on the other hand it
> > means more IO wait.
>
> Hm, if all tasks are waiting for memory, what is stopping kswapd
> to run? :)

Suppose you have 8 high-priority tasks waiting on kswapd
and one lower-priority (but still higher than kswapd)
process running and preventing kswapd from doing its work.
Oh .. and also preventing the higher-priority tasks from
being woken up and continuing...

Rik
--
Virtual memory is like a game you can't win;
However, without VM there's truly nothing to lose...

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