On Fri, May 13, 2011 at 12:15:06AM +0200, Johannes Weiner 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. It'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. I've loaded up the > > system, and taken the tar load generator through three runs without > > producing a spinning kswapd (this is PREEMPT). I'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(). I'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. If it returns true, kswapd will keep running. So if > pgdat_balanced() returns true, kswapd should go to sleep. > > This? > You're right. > 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, > * must be balanced > */ > if (order) > - return pgdat_balanced(pgdat, balanced, classzone_idx); > + return !pgdat_balanced(pgdat, balanced, classzone_idx); > else > return !all_zones_ok; > } -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
