On Sat, Jul 13, 2013 at 07:23:58AM +0800, Hush Bensen wrote: > Do you mean your patch done this fair? There is target zone shrink as > you mentiond in the vanilla kernel, however, your patch also done target > compaction/reclaim, is this fair? It's still not fair, zone_reclaim_mode cannot be (modulo major rework at least) as its whole point is to reclaim memory from the local node indefinitely, even if there's plenty of "free" or "reclaimable" memory in remote nodes. But waking kswapd before all nodes are below the low wmark probably would make it even less fair than it is now, or at least it wouldn't provide a fariness increase. The idea of allowing allocations in the min-low wmark range is that the "low" wmark would be restored soon anyway at the next zone_reclaim() invocation, and the zone_reclaim will still behave synchronous (like direct reclaim) without ever waking kswapd, regardless if we stop at the low or at the min. But if we stop at the "low" we're more susceptible to parallel allocation jitters as the jitter-error margin then becomes: .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX), which is just 1 single high order page in case of (1<<order) >= SWAP_CLUSTER_MAX. While if we use the "min" wmark after a successful zone_reclaim(zone) to decide if to allocate from the zone (the one passed to zone_reclaim, we may have more margin for allocation jitters in other CPUs of the same node, or interrupts. So this again is connected to altering the wmark calculation for high order pages in the previous patch (which also is intended to allow having more than 1 THP page in the low-min wmark range). We don't need many, too many is just a waste of CPU, but a few more than 1 significantly improves the NUMA locality on first allocation if all CPUs in the node are allocating memory at the same time. I also trimmed down to zero the high order page requirement for the min wmark, as we don't need to guarantee hugepage availability for PF_MEMALLOC (which avoids useless compaction work). -- 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>