On Thu, Jul 14, 2011 at 12:20:38PM +0900, KOSAKI Motohiro wrote: > (2011/07/13 20:10), Mel Gorman wrote: > > On Wed, Jul 13, 2011 at 09:42:39AM +0900, KOSAKI Motohiro wrote: > >> (2011/07/11 22:01), Mel Gorman wrote: > >>> With zone_reclaim_mode enabled, it's possible for zones to be considered > >>> full in the zonelist_cache so they are skipped in the future. If the > >>> process enters direct reclaim, the ZLC may still consider zones to be > >>> full even after reclaiming pages. Reconsider all zones for allocation > >>> if direct reclaim returns successfully. > >>> > >>> Signed-off-by: Mel Gorman <mgorman@xxxxxxx> > >> > >> Hmmm... > >> > >> I like the concept, but I'm worry about a corner case a bit. > >> > >> If users are using cpusets/mempolicy, direct reclaim don't scan all zones. > >> Then, zlc_clear_zones_full() seems too aggressive operation. > > > > As the system is likely to be running slow if it is in direct reclaim > > that the complexity of being careful about which zone was cleared was > > not worth it. > > > >> Instead, couldn't we turn zlc->fullzones off from kswapd? > >> > > > > Which zonelist should it clear (there are two) and when should it > > happen? If it clears it on each cycle around balance_pgdat(), there > > is no guarantee that it'll be cleared between when direct reclaim > > finishes and an attempt is made to allocate. > > Hmm.. > > Probably I'm now missing the point of this patch. Why do we need > to guarantee tightly coupled zlc cache and direct reclaim? Because direct reclaim may free enough memory such that the zlc cache stating the zone is full is wrong. > IIUC, > zlc cache mean "to avoid free list touch if they have no free mem". > So, any free page increasing point is acceptable good, I thought. > In the other hand, direct reclaim finishing has no guarantee to > zones of zonelist have enough free memory because it has bailing out logic. > It has no guarantee but there is a reasonable expectation that direct reclaim will free some memory that means we should reconsider the zone for allocation. > So, I think we don't need to care zonelist, just kswapd turn off > their own node. > I don't understand what you mean by this. > And, just curious, If we will have a proper zlc clear point, why > do we need to keep HZ timeout? > Yes because we are not guaranteed to call direct reclaim either. Memory could be freed by a process exiting and I'd rather not add cost to the free path to find and clear all zonelists referencing the zone the page being freed belongs to. -- Mel Gorman SUSE Labs -- 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>