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? -- Michal Hocko SUSE Labs
