On Thu, Jan 27, 2011 at 04:27:55PM +0100, Andrea Arcangeli wrote: > On Thu, Jan 27, 2011 at 01:40:58PM +0000, Mel Gorman wrote: > > On Wed, Jan 26, 2011 at 05:42:37PM +0000, Mel Gorman wrote: > > > On Wed, Jan 26, 2011 at 04:36:55PM +0000, Mel Gorman wrote: > > > > > But the wmarks don't > > > > > seem the real offender, maybe it's something related to the tiny pci32 > > > > > zone that materialize on 4g systems that relocate some little memory > > > > > over 4g to make space for the pci32 mmio. I didn't yet finish to debug > > > > > it. > > > > > > > > > > > > > This has to be it. What I think is happening is that we're in balance_pgdat(), > > > > the "Normal" zone is never hitting the watermark and we constantly call > > > > "goto loop_again" trying to "rebalance" all zones. > > > > > > > > > > Confirmed. > > > <SNIP> > > > > How about the following? Functionally it would work but I am concerned > > that the logic in balance_pgdat() and kswapd() is getting out of hand > > having being adjusted to work with a number of corner cases already. In > > the next cycle, it could do with a "do-over" attempt to make it easier > > to follow. > > That number 8 is the problem, Agreed, I considered your approach as well. I didn't go with it because it was the main heuristic that allowed kswapd to skip a zone but still allows kswapd to keep going. I made the choice to try and put kswapd to sleep sooner. > I don't think anybody was ever supposed > to free 8*highwmark pages. kswapd must work in the hysteresis range > low->high area and then sleep wait low to hit again before it gets > wakenup. Not sure how that number 8 ever come up... but to be it looks > like the real offender and I wouldn't work around it. > It was introduced by commit [32a4330d: mm: prevent kswapd from freeing excessive amounts of lowmem] and sure enough, it was intended to avoid a situation where memory was freed from every zone if one was imbalanced - sounds familiar. > totally untested... I will test.... > It should work in terms of free memory. When testing, monitor as well if kswapd is going asleep or if it is stuck in D state. If it's stuck in D state, it's looping around in balance_pgdat() and consuming CPU for no good reason (can use vmscan tracepoints to confirm). -- Mel Gorman Linux Technology Center IBM Dublin Software Lab -- 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 policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>