Minchan Kim <minchan@xxxxxxxxxx> writes: > Hi, > > On Thu, Jan 05, 2017 at 09:33:55AM +0800, Huang, Ying wrote: >> Hi, Minchan, >> >> Minchan Kim <minchan@xxxxxxxxxx> writes: >> [snip] >> > >> > The patchset has used several techniqueus to reduce lock contention, for example, >> > batching alloc/free, fine-grained lock and cluster distribution to avoid cache >> > false-sharing. Each items has different complexity and benefits so could you >> > show the number for each step of pathchset? It would be better to include the >> > nubmer in each description. It helps how the patch is important when we consider >> > complexitiy of the patch. >> >> Here is the test data. > > Thanks! > >> >> We test the vm-scalability swap-w-seq test case with 32 processes on a >> Xeon E5 v3 system. The swap device used is a RAM simulated PMEM >> (persistent memory) device. To test the sequential swapping out, the >> test case created 32 processes, which sequentially allocate and write to >> the anonymous pages until the RAM and part of the swap device is used >> up. >> >> The patchset is rebased on v4.9-rc8. So the baseline performance is as >> follow, >> >> "vmstat.swap.so": 1428002, > > What does it mean? vmstat.pswpout? This is the average of swap.so column of /usr/bin/vmstat output. We run /usr/bin/vmstat with, /usr/bin/vmstat -n 1 >> "perf-profile.calltrace.cycles-pp._raw_spin_lock_irq.__add_to_swap_cache.add_to_swap_cache.add_to_swap.shrink_page_list": 13.94, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock_irqsave.__remove_mapping.shrink_page_list.shrink_inactive_list.shrink_node_memcg": >> 13.75, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock.swap_info_get.swapcache_free.__remove_mapping.shrink_page_list": 7.05, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock.swap_info_get.page_swapcount.try_to_free_swap.swap_writepage": 7.03, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock.__swap_duplicate.swap_duplicate.try_to_unmap_one.rmap_walk_anon": 7.02, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock.get_swap_page.add_to_swap.shrink_page_list.shrink_inactive_list": 6.83, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock.page_check_address_transhuge.page_referenced_one.rmap_walk_anon.rmap_walk": 0.81, > > Numbers mean overhead percentage reported by perf? Yes. >> >> Patch 1 is a clean up patch. >> > >> > Could it be separated patch? >> > >> >> Patch 2 creates a lock per cluster, this gives us a more fine graind lock >> >> that can be used for accessing swap_map, and not lock the whole >> >> swap device >> >> After patch 2, the result is as follow, >> >> "vmstat.swap.so": 1481704, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock_irq.__add_to_swap_cache.add_to_swap_cache.add_to_swap.shrink_page_list": 27.53, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock_irqsave.__remove_mapping.shrink_page_list.shrink_inactive_list.shrink_node_memcg": >> 27.01, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock.free_pcppages_bulk.drain_pages_zone.drain_pages.drain_local_pages": 1.03, >> >> The swap out throughput is at the same level, but the lock contention on >> swap_info_struct->lock is eliminated. >> >> >> Patch 3 splits the swap cache radix tree into 64MB chunks, reducing >> >> the rate that we have to contende for the radix tree. >> > >> >> After patch 3, >> >> "vmstat.swap.so": 2050097, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock.get_swap_page.add_to_swap.shrink_page_list.shrink_inactive_list": 43.27, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock.get_page_from_freelist.__alloc_pages_nodemask.alloc_pages_vma.handle_mm_fault": 4.84, >> >> The swap out throughput is improved about ~43% compared with baseline. >> The lock contention on swap cache radix tree lock is eliminated. >> swap_info_struct->lock in get_swap_page() becomes the most heavy >> contended lock. > > The numbers are great! Please include those into each patchset. > And I ask one more thing I said earlier about patch 2. > > "" > I hope you make three steps to review easier. You can create some functions like > swap_map_lock and cluster_lock which are wrapper functions just hold swap_lock. > It doesn't change anything performance pov but it clearly shows what kinds of lock > we should use in specific context. > > Then, you can introduce more fine-graind lock in next patch and apply it into > those wrapper functions. > > And last patch, you can adjust cluster distribution to avoid false-sharing. > And the description should include how it's bad in testing so it's worth. > "" > > It makes review more easier, I believe. Sorry, personally, I don't like this way to organize the patchset. So unless more people have this requirement, I still want to keep the current way. Best Regards, Huang, Ying >> >> > >> >> Patch 4 eliminates unnecessary page allocation for read ahead. >> > >> > Could it be separated patch? >> > >> >> Patch 5-9 create a per cpu cache of the swap slots, so we don't have >> >> to contend on the swap device to get a swap slot or to release >> >> a swap slot. And we allocate and release the swap slots >> >> in batches for better efficiency. >> >> After patch 9, >> >> "vmstat.swap.so": 4170746, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock.swapcache_free_entries.free_swap_slot.free_swap_and_cache.unmap_page_range": 13.91, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock.get_page_from_freelist.__alloc_pages_nodemask.alloc_pages_vma.handle_mm_fault": 8.56, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock.get_page_from_freelist.__alloc_pages_slowpath.__alloc_pages_nodemask.alloc_pages_vma": >> 2.56, >> "perf-profile.calltrace.cycles-pp._raw_spin_lock.get_swap_pages.get_swap_page.add_to_swap.shrink_page_list": 2.47, >> >> The swap out throughput is improved about 192% compared with the >> baseline. There are still some lock contention for >> swap_info_struct->lock, but the pressure begins to shift to buddy system >> now. >> >> Best Regards, >> Huang, Ying >> >> -- >> 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> -- 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>