Ext3 IO context

[Pradeep Vincent]

I am running a BDB based application on top of EXT3 on Linux (RH 7.2)
- the application and the configuration are exactly the same. When the
application writes, sometimes the IO happens in the context of the
application thread while most of the time the IO happens in the
context kjournald.
 What does it mean for IO to happen in initiating process context for
non O_SYNC file I/O. I was thinking the dirty file cache thresholds
determine if a write to a filesystem write will correspond to block
I/O in the process context. Is that how ext3 works. I am not very
familiar with kjournald functionality - is that thread meant to
initiate I/O just for metadata updates or for data updates as well ?

I figured out the process context for I/Os using

sysctl -w vm.block_dump='1' which throws debug messages into kern.log.

Please cc pradeep.vincent at gmail.com

Thanks,

Pradeep Vincent