Major changes from v2: o Split patchset into two parts, one is for replacing compaction deferring with compaction limit and the other is for changing scanner activity o Add some fixes and cleanup for current defer logic o Fix opposite direction problem in "skip useless pfn when..." patch o Reuse current defer logic for compaction limit o Provide proper argument when calling __reset_isolation_suitable() o Prevent async compaction while compaction limit is activated Previous cover-letter isn't appropriate for this part1 patchset so I just append link about it. https://lkml.org/lkml/2015/8/23/182 New description: Compaction deferring effectively reduces compaction overhead if compaction success isn't expected. But, it is implemented that skipping a number of compaction requests until compaction is re-enabled. Due to this implementation, unfortunate compaction requestor will get whole compaction overhead unlike others have zero overhead. And, after deferring start to work, even if compaction success possibility is restored, we should skip to compaction in some number of times. This patch try to solve above problem by using compaction limit. Instead of imposing compaction overhead to one unfortunate requestor, compaction limit distributes overhead to all compaction requestors. All requestors have a chance to migrate some amount of pages and after limit is exhausted compaction will be stopped. This will fairly distributes overhead to all compaction requestors. And, because we don't defer compaction request, someone will succeed to compact as soon as possible if compaction success possiblility is restored. I tested this patch on my compaction benchmark and found that high-order allocation latency is evenly distributed and there is no latency spike in the situation where compaction success isn't possible. Following is the result of each high-order allocation latency (ns). Base vs Limit 9807 failure 825 9807 failure 10839 9808 failure 820 9808 failure 9762 9809 failure 827 9809 failure 8585 9810 failure 3751 9810 failure 14052 9811 failure 881 9811 failure 10781 9812 failure 827 9812 failure 9906 9813 failure 2447430 9813 failure 8925 9814 failure 8632 9814 failure 9185 9815 failure 1172 9815 failure 9076 9816 failure 1045 9816 failure 10860 9817 failure 1044 9817 failure 10571 9818 failure 1043 9818 failure 8789 9819 failure 979 9819 failure 9086 9820 failure 4338 9820 failure 43681 9821 failure 1001 9821 failure 9361 9822 failure 875 9822 failure 15175 9823 failure 822 9823 failure 9394 9824 failure 827 9824 failure 334341 9825 failure 829 9825 failure 15404 9826 failure 823 9826 failure 10419 9827 failure 824 9827 failure 11375 9828 failure 827 9828 failure 9416 9829 failure 822 9829 failure 9303 9830 failure 3646 9830 failure 18514 9831 failure 869 9831 failure 11064 9832 failure 820 9832 failure 9626 9833 failure 832 9833 failure 8794 9834 failure 820 9834 failure 10576 9835 failure 2450955 9835 failure 12260 9836 failure 9428 9836 failure 9049 9837 failure 1067 9837 failure 10346 9838 failure 968 9838 failure 8793 9839 failure 984 9839 failure 8932 9840 failure 4262 9840 failure 18436 9841 failure 964 9841 failure 11429 9842 failure 937 9842 failure 9433 9843 failure 828 9843 failure 8838 9844 failure 827 9844 failure 8948 9845 failure 822 9845 failure 13017 9846 failure 827 9846 failure 10795 As you can see, Base has a latency spike periodically, but, in Limit, latency is distributed evenly. This patchset is based on linux-next-20151106 + "restore COMPACT_CLUSTER_MAX to 32" + "__compact_pgdat() code cleanuup" which are sent by me today. Thanks. Joonsoo Kim (7): mm/compaction: skip useless pfn when updating cached pfn mm/compaction: remove unused defer_compaction() in compaction.h mm/compaction: initialize compact_order_failed to MAX_ORDER mm/compaction: update defer counter when allocation is expected to succeed mm/compaction: respect compaction order when updating defer counter mm/compaction: introduce migration scan limit mm/compaction: replace compaction deferring with compaction limit include/linux/compaction.h | 3 - include/linux/mmzone.h | 6 +- include/trace/events/compaction.h | 7 +- mm/compaction.c | 188 ++++++++++++++++++++++++-------------- mm/internal.h | 1 + mm/page_alloc.c | 4 +- 6 files changed, 125 insertions(+), 84 deletions(-) -- 1.9.1 -- 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>