Thinko in kswapd?

[Stephen C. Tweedie]

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Hi,

There is what appears to be a simple thinko in kswapd.  We really
ought to keep kswapd running as long as there is either a free space
or an inactive page shortfall; but right now we only keep going if
_both_ are short.

Diff below.  With this change, I've got a 64MB box running Applix and
Star Office with multiple open documents plus a few other big apps
running, and switching desktops or going between documents is once
more nice and snappy.  Running a normal heavily populated desktop in
256MB used to be painful, with much apparently unnecessary swapping,
if we had background page-cache intensive operations (eg find|wc)
going on: the patched kernel feels much better interactively,
presumably because kswapd is now doing the work it is supposed to do,
instead of forcing normal apps to go into page stealing mode
themselves.

--Stephen

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--- mm/vmscan.c.~1~	Fri Mar 16 15:39:24 2001
+++ mm/vmscan.c	Thu Mar 22 13:05:37 2001
@@ -1010,7 +1010,7 @@
 		 * We go to sleep for one second, but if it's needed
 		 * we'll be woken up earlier...
 		 */
-		if (!free_shortage() || !inactive_shortage()) {
+		if (!free_shortage() && !inactive_shortage()) {
 			interruptible_sleep_on_timeout(&kswapd_wait, HZ);
 		/*
 		 * If we couldn't free enough memory, we see if it was

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