I want to record with the ceph-devel archive results from testing limits of 
xattrs for Linux filesystems used with Ceph.

Script that creates xattrs with name user.test1, user.test2, …. on a single file
3.10 linux kernel

ext4  
value bytes       number of entries
    1               148
   16             103
  256          14
  512            7
  1024         3
4036          1 
Beyond this immediately get ENOSPC

btrfs    
value bytes       number of entries
 8                       10k
16                      10k
32                       10k
64                       10k
128                      10k
256                      10k
512                     10k  slow but worked 1,000,000 got completely hung for 
minutes at a time during removal strace showed no forward progress
1024             10k
2048             10k
 3096            10k
Beyond this you start getting ENOSPC after fewer entries

xfs (limit entries due to xfs crash with 10k entries)
value bytes       number of entries
1                       1k
8                        1k
16                       1k
32                       1k
64                      1k
128              1k
256                     1k
512              1k
1024            1k
2048             1k
4096             1k
8192             1k
16384                    1k
32768                    1k
65536                    1k

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