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

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

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

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

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I've took both on tests. The subject is acp and spd_readdir used =

with

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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_ex=

t4_readir.png

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3) both: http://91.234.146.107/~difrost/seekwatcher/acp_vs_spd_ex=

t4.png

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The acp looks much better than spd_readdir but directory copy wit=

h

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spd_readdir decreased to 52m 39sec (30 min less).

Do you have stats on how big these files are, and how fragmented t=

hey

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are? =A0For acp and spd to give us this, I think something has gon=

e wrong

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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. =A0(The ext4 crowd may have bett=

er

suggestions on measuring fragmentation).

Since you mention this is a compile farm, I'm guessing there are a bu=

nch

of .o files created by parallel builds. =A0There 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
=46iles 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.p=
ng
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