2012/3/2 Chris Mason [off-list ref]:

On Fri, Mar 02, 2012 at 03:16:12PM +0100, Jacek Luczak wrote:

quoted

2012/3/2 Chris Mason [off-list ref]:

quoted

On Fri, Mar 02, 2012 at 11:05:56AM +0100, Jacek Luczak wrote:

quoted

I've took both on tests. The subject is acp and spd_readdir used with
tar, all on ext4:
1) acp: http://91.234.146.107/~difrost/seekwatcher/acp_ext4.png
2) spd_readdir: http://91.234.146.107/~difrost/seekwatcher/tar_ext4_readir.png
3) both: http://91.234.146.107/~difrost/seekwatcher/acp_vs_spd_ext4.png

The acp looks much better than spd_readdir but directory copy with
spd_readdir decreased to 52m 39sec (30 min less).

Do you have stats on how big these files are, and how fragmented they
are?  For acp and spd to give us this, I think something has gone wrong
at writeback time (creating individual fragmented files).

How big? Which files?

All the files you're reading ;)

filefrag will tell you how many extents each file has, any file with
more than one extent is interesting.  (The ext4 crowd may have better
suggestions on measuring fragmentation).

Since you mention this is a compile farm, I'm guessing there are a bunch
of .o files created by parallel builds.  There are a lot of chances for
delalloc and the kernel writeback code to do the wrong thing here.

This took some time be here it goes ...

* B size files - total: 1064462 (53.81%)
| Size range    | File cnt      | Fragmented    | Fragmented %  |
| [0,100)       | 288702        | 0             | 0             |
| [100,200)     | 165997        | 0             | 0             |
| [200,300)     | 45993         | 0             | 0             |
| [300,400)     | 64883         | 0             | 0             |
| [400,500)     | 39282         | 0             | 0             |
| [500,600)     | 61612         | 0             | 0             |
| [600,700)     | 208822        | 0             | 0             |
| [700,800)     | 64016         | 0             | 0             |
| [800,900)     | 58181         | 0             | 0             |
| [900,1024)    | 66974         | 0             | 0             |

* K size files - total: 907375 (45.86%)
| Size range    | File cnt      | Fragmented    | Fragmented %  |
| [1,2)         | 285481        | 0             | 0             |
| [2,3)         | 148461        | 0             | 0             |
| [3,4)         | 102569        | 0             | 0             |
| [4,5)         | 45089         | 0             | 0             |
| [5,6)         | 44223         | 0             | 0             |
| [6,10)        | 94202         | 0             | 0             |
| [10,20)       | 83760         | 0             | 0             |
| [20,30)       | 42548         | 0             | 0             |
| [30,40)       | 15274         | 0             | 0             |
| [40,50)       | 4060          | 0             | 0             |
| [50,60)       | 3517          | 0             | 0             |
| [60,100)      | 7834          | 0             | 0             |
| [100,1024)    | 30357         | 0             | 0             |

*M size files - total: 6312 (0.33%)
| Size range    | File cnt      | Fragmented    | Fragmented %  |
| [1.10)        | 5806          | 100           | 1.72          |
| [10,100)      | 482           | 200           | 41.49         |
| [100,1024)    | 24            | 13            | 54.16         |

All files scanned: 1978149
Files fragmented: 313 (0.015%) where 11 have 3+ extents
Total size of fragmented files: 7GB (~13% of dir size)

tar cf on fragmented files:
1) time: 7sec
2) sw graph: http://91.234.146.107/~difrost/seekwatcher/tar_fragmented.png
3) sw graph with spd_readdir:
http://91.234.146.107/~difrost/seekwatcher/tar_fragmented_spd.png
4) both on one:
http://91.234.146.107/~difrost/seekwatcher/tar_fragmented_pure_spd.png

tar cf of fragmented files disturbed with [40,50) K files (in total
4373 files). K files before fragmented M files:
1) size: 7.2GB
2) time: 1m 14sec
3) sw graph: http://91.234.146.107/~difrost/seekwatcher/tar_disturbed.png
4) sw graph with spd_readdir:
http://91.234.146.107/~difrost/seekwatcher/tar_disturbed_spd.png
5) both on one:
http://91.234.146.107/~difrost/seekwatcher/tar_disturbed_pure_spd.png

I will perform same tests on btrfs tomorrow.

-Jacek