On Fri, 7 Apr 2017 14:49:01 +0800 "Huang, Ying" <ying.huang@xxxxxxxxx> wrote: > To reduce the lock contention of swap_info_struct->lock when freeing > swap entry. The freed swap entries will be collected in a per-CPU > buffer firstly, and be really freed later in batch. During the batch > freeing, if the consecutive swap entries in the per-CPU buffer belongs > to same swap device, the swap_info_struct->lock needs to be > acquired/released only once, so that the lock contention could be > reduced greatly. But if there are multiple swap devices, it is > possible that the lock may be unnecessarily released/acquired because > the swap entries belong to the same swap device are non-consecutive in > the per-CPU buffer. > > To solve the issue, the per-CPU buffer is sorted according to the swap > device before freeing the swap entries. Test shows that the time > spent by swapcache_free_entries() could be reduced after the patch. > > Test the patch via measuring the run time of swap_cache_free_entries() > during the exit phase of the applications use much swap space. The > results shows that the average run time of swap_cache_free_entries() > reduced about 20% after applying the patch. "20%" is useful info, but it is much better to present the absolute numbers, please. If it's "20% of one nanosecond" then the patch isn't very interesting. If it's "20% of 35 seconds" then we know we have more work to do. If there is indeed still a significant problem here then perhaps it would be better to move the percpu swp_entry_t buffer into the per-device structure swap_info_struct, so it becomes "per cpu, per device". That way we should be able to reduce contention further. Or maybe we do something else - it all depends upon the significance of this problem, which is why a full description of your measurements is useful. -- 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>
