Bug 753486

Description of problem:
Transferring a large amount of data (e.g. copying music library, or live USB image) to a slow (< 3 MB/s or so) USBMS device (typically formatted vfat) ends up slowing down the entire system, blocking I/O on other, much faster devices (such as USB- or SATA-attached discs), and producing O(minute) latencies in other processes. This renders the desktop effectively unusable until the slow I/O process completes.

Version-Release number of selected component (if applicable):
kernel-2.6.40.8-4.fc15.x86_64

How reproducible:
Always.

Steps to Reproduce:
1. Find a slow (< around 3 MB/s) USBMS device, formatted vfat.
2. Run liveusb-creator and turn it into a Fedora 16 live stick.
3. Watch as Firefox becomes unresponsive, and launching new programs takes ages.
  
Actual results:
Latency goes through the roof:

 - Firefox just stops responding.
 - Launching a new program takes much longer than is acceptable, for instance
   taking minutes instead of seconds under other circumstances (or I/O load
   to much faster devices).
 - Processes that are doing it all in memory seem unaffected (until they
   try to access a disc).

Expected results:
That a single process using a slow USBMS device is not able to hose the entire system to the extent observed, where faster, independent discs are left waiting for writes to complete to a much slower device.