On 15.11.18 09:30, Michal Hocko wrote: > On Thu 15-11-18 15:53:56, Baoquan He wrote: >> On 11/15/18 at 08:30am, Michal Hocko wrote: >>> On Thu 15-11-18 13:10:34, Baoquan He wrote: >>>> On 11/14/18 at 04:00pm, Michal Hocko wrote: >>>>> On Wed 14-11-18 22:52:50, Baoquan He wrote: >>>>>> On 11/14/18 at 10:01am, Michal Hocko wrote: >>>>>>> I have seen an issue when the migration cannot make a forward progress >>>>>>> because of a glibc page with a reference count bumping up and down. Most >>>>>>> probable explanation is the faultaround code. I am working on this and >>>>>>> will post a patch soon. In any case the migration should converge and if >>>>>>> it doesn't do then there is a bug lurking somewhere. >>>>>>> >>>>>>> Failing on ENOMEM is a questionable thing. I haven't seen that happening >>>>>>> wildly but if it is a case then I wouldn't be opposed. >>>>>> >>>>>> Applied your debugging patches, it helps a lot to printing message. >>>>>> >>>>>> Below is the dmesg log about the migrating failure. It can't pass >>>>>> migrate_pages() and loop forever. >>>>>> >>>>>> [ +0.083841] migrating pfn 10fff7d0 failed >>>>>> [ +0.000005] page:ffffea043ffdf400 count:208 mapcount:201 mapping:ffff888dff4bdda8 index:0x2 >>>>>> [ +0.012689] xfs_address_space_operations [xfs] >>>>>> [ +0.000030] name:"stress" >>>>>> [ +0.004556] flags: 0x5fffffc0000004(uptodate) >>>>>> [ +0.007339] raw: 005fffffc0000004 ffffc900000e3d80 ffffc900000e3d80 ffff888dff4bdda8 >>>>>> [ +0.009488] raw: 0000000000000002 0000000000000000 000000cb000000c8 ffff888e7353d000 >>>>>> [ +0.007726] page->mem_cgroup:ffff888e7353d000 >>>>>> [ +0.084538] migrating pfn 10fff7d0 failed >>>>>> [ +0.000006] page:ffffea043ffdf400 count:210 mapcount:201 mapping:ffff888dff4bdda8 index:0x2 >>>>>> [ +0.012798] xfs_address_space_operations [xfs] >>>>>> [ +0.000034] name:"stress" >>>>>> [ +0.004524] flags: 0x5fffffc0000004(uptodate) >>>>>> [ +0.007068] raw: 005fffffc0000004 ffffc900000e3d80 ffffc900000e3d80 ffff888dff4bdda8 >>>>>> [ +0.009359] raw: 0000000000000002 0000000000000000 000000cb000000c8 ffff888e7353d000 >>>>>> [ +0.007728] page->mem_cgroup:ffff888e7353d000 >>>>> >>>>> I wouldn't be surprised if this was a similar/same issue I've been >>>>> chasing recently. Could you try to disable faultaround to see if that >>>>> helps. It seems that it helped in my particular case but I am still >>>>> waiting for the final good-to-go to post the patch as I do not own the >>>>> workload which triggered that issue. >>>> >>>> Tried, still stuck in last block sometime. Usually after several times >>>> of hotplug/unplug. If stop stress program, the last block will be >>>> offlined immediately. >>> >>> Is the pattern still the same? I mean failing over few pages with >>> reference count jumping up and down between attempts? >> >> ->count jumping up and down, mapcount stays the same value. >> >>> >>>> [root@ ~]# cat /sys/kernel/debug/fault_around_bytes >>>> 4096 >>> >>> Can you make it 0? >> >> I executed 'echo 0 > fault_around_bytes', value less than one page size >> will round up to one page. > > OK, I have missed that. So then there must be a different source of the > page count volatility. Is it always the same file? > > I think we can rule out memory reclaim because that depends on the page > lock. Is the stress test hitting on memory compaction? In other words, > are > grep compact /proc/vmstat > counters changing during the offline test heavily? I am asking because I > do not see compaction pfn walkers skipping over MIGRATE_ISOLATE > pageblocks. But I might be missing something easily. > > It would be also good to find out whether this is fs specific. E.g. does > it make any difference if you use a different one for your stress > testing? > I am wondering why it is always the last memory block of that device (and even that node). Coincidence? -- Thanks, David / dhildenb
