On Wed, 2011-07-20 at 00:51 +0800, Minchan Kim wrote: > On Tue, Jul 19, 2011 at 04:53:04PM +0800, Shaohua Li wrote: > > On Tue, 2011-07-19 at 16:45 +0800, Minchan Kim wrote: > > > On Tue, Jul 19, 2011 at 4:09 PM, Shaohua Li <shaohua.li@xxxxxxxxx> wrote: > > > > I'm running a workload which triggers a lot of swap in a machine with 4 nodes. > > > > After I kill the workload, I found a kswapd livelock. Sometimes kswapd3 or > > > > kswapd2 are keeping running and I can't access filesystem, but most memory is > > > > free. This looks like a regression since commit 08951e545918c159. > > > > > > Could you tell me what is 08951e545918c159? > > > You mean [ebd64e21ec5a, > > > mm-vmscan-only-read-new_classzone_idx-from-pgdat-when-reclaiming-successfully] > > > ? > > ha, sorry, I should copy the commit title. > > 08951e545918c159(mm: vmscan: correct check for kswapd sleeping in > > sleeping_prematurely) > > > > I don't mean it. In my bogus git tree, I can't find it but I can look at it in repaired git tree. :) > Anyway, I have a comment. Please look at below. > > On Tue, Jul 19, 2011 at 03:09:27PM +0800, Shaohua Li wrote: > > I'm running a workload which triggers a lot of swap in a machine with 4 nodes. > > After I kill the workload, I found a kswapd livelock. Sometimes kswapd3 or > > kswapd2 are keeping running and I can't access filesystem, but most memory is > > free. This looks like a regression since commit 08951e545918c159. > > Node 2 and 3 have only ZONE_NORMAL, but balance_pgdat() will return 0 for > > classzone_idx. The reason is end_zone in balance_pgdat() is 0 by default, if > > all zones have watermark ok, end_zone will keep 0. > > Later sleeping_prematurely() always returns true. Because this is an order 3 > > wakeup, and if classzone_idx is 0, both balanced_pages and present_pages > > in pgdat_balanced() are 0. > > Sigh. Yes. > > > We add a special case here. If a zone has no page, we think it's balanced. This > > fixes the livelock. > > Yes. Your patch can fix it but I don't like that it adds handling special case. > (Although Andrew merged quickly). The special case is reasonable, because if a zone has no page, it should be considered balanced. > The problem is to return 0-classzone_idx if all zones was okay. > So how about this? My original implementation is like this (I return a populated zone with minimum zone index). But I changed my mind later. the end_zone is zone we work, so return 0 is reasonable, because all zones are ok. Maybe we should return -1 if all zones are ok, but this is another story. > This can change old behavior slightly. > For example, if balance_pgdat calls with order-3 and all zones are okay about order-3, > it will recheck order-0 as end_zone isn't 0 any more. > But I think it's desriable side effect we have missed. if order-3 is ok, order-0 is ok too I think, so the check is unnecessary. Thanks, Shaohua -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>