On Tue, Mar 19, 2013 at 11:08:23AM +0800, Simon Jeons wrote: > Hi Mel, > On 03/17/2013 09:04 PM, Mel Gorman wrote: > >kswapd stops raising the scanning priority when at least SWAP_CLUSTER_MAX > >pages have been reclaimed or the pgdat is considered balanced. It then > >rechecks if it needs to restart at DEF_PRIORITY and whether high-order > >reclaim needs to be reset. This is not wrong per-se but it is confusing > > per-se is short for what? > It means "in self" or "as such". > >to follow and forcing kswapd to stay at DEF_PRIORITY may require several > >restarts before it has scanned enough pages to meet the high watermark even > >at 100% efficiency. This patch irons out the logic a bit by controlling > >when priority is raised and removing the "goto loop_again". > > > >This patch has kswapd raise the scanning priority until it is scanningmm: vmscan: Flatten kswapd priority loop > >enough pages that it could meet the high watermark in one shrink of the > >LRU lists if it is able to reclaim at 100% efficiency. It will not raise > > Which kind of reclaim can be treated as 100% efficiency? > 100% efficiency is where every page scanned can be reclaimed immediately. > > /* > >- * We do this so kswapd doesn't build up large priorities for > >- * example when it is freeing in parallel with allocators. It > >- * matches the direct reclaim path behaviour in terms of impact > >- * on zone->*_priority. > >+ * Fragmentation may mean that the system cannot be rebalanced > >+ * for high-order allocations in all zones. If twice the > >+ * allocation size has been reclaimed and the zones are still > >+ * not balanced then recheck the watermarks at order-0 to > >+ * prevent kswapd reclaiming excessively. Assume that a > >+ * process requested a high-order can direct reclaim/compact. > > */ > >- if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX) > >- break; > >- } while (--sc.priority >= 0); > >+ if (order && sc.nr_reclaimed >= 2UL << order) > >+ order = sc.order = 0; > > If order == 0 is meet, should we do defrag for it? > Compaction is unnecessary for order-0. -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>