Messages in this thread | | | Subject | Re: [PATCHSET v3][RFC] Make background writeback not suck | From | Holger Hoffstätte <> | Date | Fri, 1 Apr 2016 18:58:00 +0200 |
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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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