[PATCH] Recent VM fiasco - fixed

From: Zlatko Calusic (zlatko@iskon.hr)
Date: Mon May 08 2000 - 12:21:20 EST

Hi to all!

After I _finally_ got tired of the constant worse and worse VM
behaviour in the recent kernels, I thought I could spare few hours
this weekend just to see what's going on. I was quite surprised to see
that VM subsystem, while at its worst condition (at least in 2.3.x),
is quite easily repairable even to unskilled ones... I compiled and
checked few kernels back to 2.3.51, and found that new code was
constantly added just to make things go worse. Short history:

2.3.51 - mostly OK, but reading from disk takes too much CPU (kswapd)
2.3.99-pre1, 2 - as .51 + aggressive swap out during writing
2.3.99-pre3, 4, 5 - reading better
2.3.99-pre5, 6 - both reading and writing take 100% CPU!!!

I also tried some pre7-x (forgot which one) but that one was f****d up
beyond a recognition (read: was killing my processes including X11
like mad, every time I started writing to disk). Thus patch that
follows, and fixes all above mentioned problems, was made against
pre6, sorry. I'll made another patch when pre7 gets out, if things are
still not properly fixed.

BTW, this patch mostly *removes* cruft recently added, and returns to
the known state of operation. After that is achieved it is then easy
to selectively add good things I might have removed, and change
behaviour as wanted, but I would like to urge people to test things
thoroughly before releasing patches this close to 2.4.

Then again, I might have introduced bugs in this patch, too. :)
But, I *tried* to break it (spent some time doing that), and testing
didn't reveal any bad behaviour.



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