Hi, Chinner, Dave Chinner <da...@fromorbit.com> writes:
> On Wed, Aug 10, 2016 at 06:00:24PM -0700, Linus Torvalds wrote: >> On Wed, Aug 10, 2016 at 5:33 PM, Huang, Ying <ying.hu...@intel.com> wrote: >> > >> > Here it is, >> >> Thanks. >> >> Appended is a munged "after" list, with the "before" values in >> parenthesis. It actually looks fairly similar. >> >> The biggest difference is that we have "mark_page_accessed()" show up >> after, and not before. There was also a lot of LRU noise in the >> non-profile data. I wonder if that is the reason here: the old model >> of using generic_perform_write/block_page_mkwrite didn't mark the >> pages accessed, and now with iomap_file_buffered_write() they get >> marked as active and that screws up the LRU list, and makes us not >> flush out the dirty pages well (because they are seen as active and >> not good for writeback), and then you get bad memory use. >> >> I'm not seeing anything that looks like locking-related. > > Not in that profile. I've been doing some local testing inside a > 4-node fake-numa 16p/16GB RAM VM to see what I can find. You run the test in a virtual machine, I think that is why your perf data looks strange (high value of _raw_spin_unlock_irqrestore). To setup KVM to use perf, you may refer to, https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Virtualization_Tuning_and_Optimization_Guide/sect-Virtualization_Tuning_Optimization_Guide-Monitoring_Tools-vPMU.html https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization_Administration_Guide/sect-perf-mon.html I haven't tested them. You may Google to find more information. Or the perf/kvm people can give you more information. > I'm yet to work out how I can trigger a profile like the one that > was reported (I really need to see the event traces), but in the > mean time I found this.... > > Doing a large sequential single threaded buffered write using a 4k > buffer (so single page per syscall to make the XFS IO path allocator > behave the same way as in 4.7), I'm seeing a CPU profile that > indicates we have a potential mapping->tree_lock issue: > > # xfs_io -f -c "truncate 0" -c "pwrite 0 47g" /mnt/scratch/fooey > wrote 50465865728/50465865728 bytes at offset 0 > 47.000 GiB, 12320768 ops; 0:01:36.00 (499.418 MiB/sec and 127850.9132 ops/sec) > > .... > > 24.15% [kernel] [k] _raw_spin_unlock_irqrestore > 9.67% [kernel] [k] copy_user_generic_string > 5.64% [kernel] [k] _raw_spin_unlock_irq > 3.34% [kernel] [k] get_page_from_freelist > 2.57% [kernel] [k] mark_page_accessed > 2.45% [kernel] [k] do_raw_spin_lock > 1.83% [kernel] [k] shrink_page_list > 1.70% [kernel] [k] free_hot_cold_page > 1.26% [kernel] [k] xfs_do_writepage Best Regards, Huang, Ying