On Wed, May 18, 2011 at 09:26:09AM +0900, KOSAKI Motohiro wrote: > >Lets see; > > > >shrink_page_list() only applies if inactive pages were isolated > > which in turn may not happen if all_unreclaimable is set in > > shrink_zones(). If for whatver reason, all_unreclaimable is > > set on all zones, we can miss calling cond_resched(). > > > >shrink_slab only applies if we are reclaiming slab pages. If the first > > shrinker returns -1, we do not call cond_resched(). If that > > first shrinker is dcache and __GFP_FS is not set, direct > > reclaimers will not shrink at all. However, if there are > > enough of them running or if one of the other shrinkers > > is running for a very long time, kswapd could be starved > > acquiring the shrinker_rwsem and never reaching the > > cond_resched(). > > OK. > > > > > >balance_pgdat() only calls cond_resched if the zones are not > > balanced. For a high-order allocation that is balanced, it > > checks order-0 again. During that window, order-0 might have > > become unbalanced so it loops again for order-0 and returns > > that was reclaiming for order-0 to kswapd(). It can then find > > that a caller has rewoken kswapd for a high-order and re-enters > > balance_pgdat() without ever have called cond_resched(). > > Then, Shouldn't balance_pgdat() call cond_resched() unconditionally? > The problem is NOT 100% cpu consumption. if kswapd will sleep, other > processes need to reclaim old pages. The problem is, kswapd doesn't > invoke context switch and other tasks hang-up. > Which the shrink_slab patch does (either version). What's the gain from sprinkling more cond_resched() around? If you think there is, submit another pair of patches (include patch 1 from this series) but I'm not seeing the advantage myself. > > >While it appears unlikely, there are bad conditions which can result > >in cond_resched() being avoided. > > > > -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
