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SubjectRe: [vm] writing to UDF DVD+RW (/dev/sr0) while under memory pressure: box ==> doorstop

On Tue, 2008-01-08 at 03:38 -0800, Andrew Morton wrote:
> On Tue, 08 Jan 2008 12:05:16 +0100 Mike Galbraith <> wrote:

> > Seeks on DVD drives are apparently far FAR more horrible that I ever
> > imagined, so writing to a filesystem on a DVD+RW in effect constitutes
> > the stupid thing I was worried about above. Make an image, populate it,
> > write it instead... sure to be a truckload faster, and due to the VM
> > connection, much safer too. Oh well.
> >
> Well. From your earlier trace it appeared that something was causing
> the filesystem to perform synchronous inode writes - sync_dirty_buffer() was
> called.
> This will cause many more seeks than would occur if we were doing full
> delayed writing, with obvious throughput implications.

Yes, with UDF, the IO was _incredibly_ slow. With ext2, it was better,
though still very bad. I tested with that other OS, and it gets ~same
throughput with UDF as I got with ext2 (ick).

UDF does udf_clear_inode() -> write_inode_now(inode, 1)

I suppose I could try write_inode_now(inode, 0). Might unstick the box.


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