Major Description
Now, we found ldiskfs(Ext4) directory creation is much slower than file creation.
Under RHEL7 with ldiskfs, we got following results.
- ./mdtest -d /mnt/test/ -n 100000 -i 3
Directory creation: 52299.122 ops/second
File creation: 106569 ops/second
As we can see, directory creation performance is much slower than file creation, after doing some profiling, we found cost differences come from following calls:
| ->ext4_mkdir() |
| ->ext4_init_new_dir() |
| ->ext4_append() |
| ->ext4_bread() |
| ->ext4_getblk() |
| ->ext4_map_blocks() So here an extra block allocation for '.' and '..' items will cost extra time, and we enable inline_data which will reduce block allocation for such case, things got better: |
Directory creation: 111276.454 ops/second
File creation: 114920.338 ops/second
As we can see, with inline_data enabled, directory creation performance is same as file creation.
We also found inline_data feature not only help directory creation but also help
directory reading, consider following case:
- creating 100W directories under test directory and then run 'time ls -R ./test'
time cost reduce from 2m25s to 30s, huge differences! this is because inline_data will reduce an extra block allocation which also speed read performance as we don't have to do an extra block IO.
In generally, Inline_data could improve performance and reduce space allocation which is also good.
As now, inline_data is include in RHEL7 and there seems some conflicts with Lustre dirdata feature, but inline_data deserve us an eye, adding it to lustre will give us some improvement thought we still confirm it under lustre.
