Re: [PATCH] ext4: Fix small file fragmentation

[Theodore Tso <tytso@mit.edu>]

Here's an interesting data point.  Using Chris Mason's compilebench:

http://oss.oracle.com/~mason/compilebench

If I use:

./compilebench  -D /mnt -i 2 -r 0

on a 4GB machine such that I have plenty of memory (and nothing gets
forced disk due to memory pressure), I don't see hardly any of the
small file fragmentation problem (0.8% of the inodes in use on the
filesystem.  This is with your patch applied.

However, if I use:

./compilebench  -D /mnt -i 10 -r 0

so that data blocks are getting pushed out due to memory pressure,
then I see plenty of non-contiugous inodes (8.1% of the inodes in use
on the filesystem).  So with your patch applied, it seems that we
still have a problem related to delayed allocation and how the VM
system is doing its page cleaning.

						- Ted