Re: More VM balancing issues..

[Linus Torvalds <torvalds@transmeta.com>]

Oh, I found another problem: when the VM balancing was rewritten, the
"pages_low" thing was still calculated, but nothing actually USED it.

So we had three water-marks: "enough for anything", "low on memory" and
"critical".

And we somehow lost the "low on memory" and only used the "enough" and
"critical" to do all comparisons.

Which makes for a _very_ choppy balance, and is definitely wrong.

The behaviour should be something like:
 - whenever we dip below "low", we wake up kswapd. kswapd remains awake
   (for that zone) until we reach "enough".
 - whenever we dip below "critical", we start doing synchronous memory
   freeing ourselves. We continue to do that until we reach "low" again
   (at which point kswapd will still continue in the background, but we
   don't depend on the synchronous freeing any more).

but for some time we appear to have gotten this wrong, and lost the "low"
mark, and used the "critical" and "high" marks only. 

Or maybe somebody did some testing and decided to disagree with the old
three-level thing based on actual numbers? The only coding I've done has
been based on "this is how I think it should work, and because I'm always
right it's obviously the way it _should_ work". Which is not always the
approach that gets the best results ;)

		Linus

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux.eu.org/Linux-MM/