Re: Linux 2.4.17 vs 2.2.19 vs rml new VM

From: Rik van Riel (
Date: Wed Jan 02 2002 - 07:25:23 EST

On Wed, 2 Jan 2002 wrote:

> I tried rmap-10 new VM and under my typical load my desktop machine
> froze repeatedly. Seemed the memory pool was going down the drain
> before the freeze. Meaning apps were failing and getting stuck in
> various odd states.

There's a stupid logic inversion bug in rmap-10, which is
fixed in rmap-10a. Andrew Morton tracked it down about an
hour after I released rmap-10.

Basically in wakeup_kswapd() user processes go to sleep
if the pressure on the VM is _really_ high *and* the user
process has all the same GFP options set as kswapd itself,
so the process can sleep on kswapd.

        if ((gfp_mask & GFP_KSWAPD) == GFP_KSWAPD)

Thinking about it, rmap-10a doesn't do the right thing,
either, releasing patches at 4 am isn't the right thing ;)

In vmscan.c, line 707 _should_ be:

        if ((gfp_mask & GFP_KSWAPD) != GFP_KSWAPD)

This way tasks which cannot safely sleep on kswapd will
return immediately, allowing only tasks which _can_
sleep on kswapd to go for a break.

Oh well, time for testing and releasing rmap-11 ;)



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