On Fri, May 13, 2011 at 7:15 AM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > On Thu, May 12, 2011 at 05:04:41PM -0500, James Bottomley wrote: >> On Thu, 2011-05-12 at 15:04 -0500, James Bottomley wrote: >> > Confirmed, I'm afraid ... I can trigger the problem with all three >> > patches under PREEMPT. ÂIt's not a hang this time, it's just kswapd >> > taking 100% system time on 1 CPU and it won't calm down after I unload >> > the system. >> >> Just on a "if you don't know what's wrong poke about and see" basis, I >> sliced out all the complex logic in sleeping_prematurely() and, as far >> as I can tell, it cures the problem behaviour. ÂI've loaded up the >> system, and taken the tar load generator through three runs without >> producing a spinning kswapd (this is PREEMPT). ÂI'll try with a >> non-PREEMPT kernel shortly. >> >> What this seems to say is that there's a problem with the complex logic >> in sleeping_prematurely(). ÂI'm pretty sure hacking up >> sleeping_prematurely() just to dump all the calculations is the wrong >> thing to do, but perhaps someone can see what the right thing is ... > > I think I see the problem: the boolean logic of sleeping_prematurely() > is odd. ÂIf it returns true, kswapd will keep running. ÂSo if > pgdat_balanced() returns true, kswapd should go to sleep. > > This? Yes. Good catch. > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 2b701e0..092d773 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2261,7 +2261,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining, > Â Â Â Â * must be balanced > Â Â Â Â */ > Â Â Â Âif (order) > - Â Â Â Â Â Â Â return pgdat_balanced(pgdat, balanced, classzone_idx); > + Â Â Â Â Â Â Â return !pgdat_balanced(pgdat, balanced, classzone_idx); > Â Â Â Âelse > Â Â Â Â Â Â Â Âreturn !all_zones_ok; > Â} > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxxx ÂFor more info on Linux MM, > see: http://www.linux-mm.org/ . > Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> > -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href