2012/3/4 Jacek Luczak [off-list ref]:

2012/3/3 Jacek Luczak [off-list ref]:

quoted

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

quoted

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.

[Most of files are B and K size]

quoted

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

BTRFS: Non of files according to filefrag are fragmented - all fit
into one extent.

quoted

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

BTRFS: tar on ext4 fragmented files
1) time: 6sec
2) sw graph: http://91.234.146.107/~difrost/seekwatcher/tar_fragmented_btrfs.png

quoted

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

BTRFS: tar on [40,50) K and ext4 fragmented
1) time: 56sec
2) sw graph: http://91.234.146.107/~difrost/seekwatcher/tar_disturbed_btrfs.png

New test I've included - randomly selected files:
- size 240MB
1) ext4 (time: 34sec) sw graph:
http://91.234.146.107/~difrost/seekwatcher/tar_random_ext4.png
2) btrfs (time: 55sec) sw graph:
http://91.234.146.107/~difrost/seekwatcher/tar_random_btrfs.png

Yet another test. The original issue is in the directory data
handling. In my case a lot of dirs are introduced due to extra .svn.
Let's then see how does tar on those dirs looks like.

Number of .svn directories: 61605
1) Ext4:
 - tar time: 10m 53sec
 - sw tar graph: http://91.234.146.107/~difrost/seekwatcher/svn_dir_ext4.png
 - sw tar graph with spd_readdir:
http://91.234.146.107/~difrost/seekwatcher/svn_dir_spd_ext4.png
2) Btrfs:
 - tar time: 4m 35sec
 - sw tar graph: http://91.234.146.107/~difrost/seekwatcher/svn_dir_btrfs.png
 - sw tar graph with ext4:
http://91.234.146.107/~difrost/seekwatcher/svn_dir_btrfs_ext4.png

IMO this is not a writeback issue (well it could be but then it mean
that it broken in general), it's not fragmentation. Sorting files in
readdir helps a bit but is still far behind the btrfs.

Any ideas? Is this a issue or the things are like they are and one
need to live with it.

-Jacek
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