Comment 15 for bug 1208993

More feedback about the problem I'm experiencing.

First some data about my system:

Kernel 3.16.0-57-generic
Ubuntu Desktop 14.4 LTS
32 bits
2GB RAM
Centrino duo

I complete my previous comment. I was performing two I/O operations before I got the problem. I couldn't repeat the problem with the first one (that I described in comment #14), but It's always repeatable with the second one. That is:

1. Connect two USB disks to my computer to make a copy from the first one (say disk A) to the second (say disk B). The amount of data to copy is 80GB.
2. Start the copy from USB disk A to B. After 75% copying, the copy seems to be stopped.

The progress bar in "copy files window" doesn't move. You can close the window by pressing "x" with the mouse pointer. You can try to shutdown the system by pressing the "Shut down..." menu option, but it doesn't respond and system keeps online. Launcher bar doesn't repond.

I have by default the next values for dirty_background_ratio and dirty_ratio:

vm.dirty_background_ratio = 5
vm.dirty_ratio = 10

It seems to be that, during the huge copy from disk A to B, memory has reached the 10% of dirty pages indicated by vm.dirty_ratio. After that all I/O operations became synchronous and block the system until dirty pages a written to disk. It's just a supposition. Pending to chek it by increasing vm.dirty_ratio (so I allow the system to performance more asynchronous writes before they block the system) and repeating the copy.