Re: Sorted writes in checkpoint

On Thu, 14 Jun 2007, Gregory Maxwell wrote:

> Linux has some instrumentation that might be useful for this testing,
> echo 1 > /proc/sys/vm/block_dump

That bit was developed for tracking down who was spinning the hard drive 
up out of power saving mode, and I was under the impression that very 
rough feature isn't useful at all here.  I just tried to track down again 
where I got that impression from, and I think it was this thread:

http://linux.slashdot.org/comments.pl?sid=231817&cid=18832379

This mentions general issues figuring out who was responsible for a write 
and specifically mentions how you'll have to reconcile two different paths 
if fsync is mixed in.  Not saying it won't work, it's just obvious using 
the block_dump output isn't a simple job.

(For anyone who would like an intro to this feature, try 
http://www.linuxjournal.com/node/7539/print and 
http://toadstool.se/journal/2006/05/27/monitoring-filesystem-activity-under-linux-with-block_dump 
)

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD