kupdate weirdness

[Miklos Szeredi <miklos@szeredi.hu>]

The following strange behavior can be observed:

1. large file is written
2. after 30 seconds, nr_dirty goes down by 1024
3. then for some time (< 30 sec) nothing happens (disk idle)
4. then nr_dirty again goes down by 1024
5. repeat from 3. until whole file is written

So basically a 4Mbyte chunk of the file is written every 30 seconds.
I'm quite sure this is not the intended behavior.

The reason seems to be that __sync_single_inode() will move the
partially written inode from s_io onto s_dirty, and sync_sb_inode()
will not splice it back onto s_io until the rest of the inodes on s_io
has been processed.

Since there will probably be a recently dirtied inode on s_io, this
will take some of time, but always less than 30 sec.

I don't know what's the easiest solution.

Any ideas?

Miklos
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