[Bugme-new] [Bug 21562] New: btrfs is dead slow due to fragmentation

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=21562

           Summary: btrfs is dead slow due to fragmentation
           Product: File System
           Version: 2.5
    Kernel Version: 2.6.36
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: btrfs
        AssignedTo: fs_btrfs at kernel-bugs.osdl.org
        ReportedBy: felipe.contreras at gmail.com
        Regression: No


Some files are constantly being modified, in order for btrfs to be useful, it
should take that into consideration. Currently files get fragmented to hell:

% cat History-old > History
% btrfs filesystem defragment /home
% echo 3 > /proc/sys/vm/drop_caches

% time dd if=History of=/dev/null && time dd if=History-old of=/dev/null
109664+0 records in
109664+0 records out
56147968 bytes (56 MB) copied, 1.90015 s, 29.5 MB/s
dd if=History of=/dev/null  0.08s user 0.29s system 15% cpu 2.458 total
109664+0 records in
109664+0 records out
56147968 bytes (56 MB) copied, 97.772 s, 574 kB/s
dd if=History-old of=/dev/null  0.07s user 0.80s system 0% cpu 1:37.79 total

Also, 'btrfs filesystem defragment' doesn't work.

Expected result: the filesystem doesn't become horribly slow with time, and
like other filesystems, no special tools are needed for that

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