"Huang, Ying" <ying.huang@xxxxxxxxx> writes: > Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes: > >> 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. > > I added memory freeing timing capability to vm-scalability test suite. > The result shows the memory freeing time reduced from 2.64s to 2.31s > (about -12.5%). The memory space to free is 96G (including swap). The machine has 144 CPU, 32G RAM, and 96G swap. The process number is 16. Best Regards, Huang, Ying > Best Regards, > Huang, Ying > >> 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>
