On 25.6.2015 20:14, Joonsoo Kim wrote: >> The long-term success rate of fragmentation avoidance depends on >> > minimsing the number of UNMOVABLE allocation requests that use a >> > pageblock belonging to another migratetype. Once such a fallback occurs, >> > that pageblock potentially can never be used for a THP allocation again. >> > >> > Lets say there is an unmovable pageblock with 500 free pages in it. If >> > the freepage scanner uses that pageblock and allocates all 500 free >> > pages then the next unmovable allocation request needs a new pageblock. >> > If one is not completely free then it will fallback to using a >> > RECLAIMABLE or MOVABLE pageblock forever contaminating it. > Yes, I can imagine that situation. But, as I said above, we already use > non-movable pageblock for migration scanner. While unmovable > pageblock with 500 free pages fills, some other unmovable pageblock > with some movable pages will be emptied. Number of freepage > on non-movable would be maintained so fallback doesn't happen. There's nothing that guarantees that the migration scanner will be emptying unmovable pageblock, or am I missing something? Worse, those pageblocks would be marked to skip by the free scanner if it isolated free pages from them, so migration scanner would skip them. -- 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>