On 04/01/16 03:01, Dave Chinner wrote:
> Can you go back to your original kernel, and lower nr_requests to 8?
Sure, did that and as expected it didn't help much. Under prolonged stress
it was actually even a bit worse than writeback throttling. IMHO that's not
really surprising either, since small queues now punish everyone and
in interactive mode I really want to e.g. start loading hundreds of small
thumbnails at once, or du a directory.
Instead of randomized aka manual/interactive testing I created a simple
stress tester:
#!/bin/sh
while [[ true ]]
do
cp bigfile bigfile.out
done
and running that in the background turns the system into a tar pit,
which is laughable when you consider that I have 24G and 8 cores.
With the writeback patchset and wb_percent=1 (yes, really!) it is almost
unnoticeable, but according to nmon still writes ~250-280 MB/s.
This is with deadline on ext4 on an older SATA-3 SSD that can still
do peak ~465 MB/s (with dd).
cheers,
Holger
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