Re: [PATCH 0/5] btrfs/282: resolve intermittent failures

David Disseldorp
2023-12-07T13:49:15Z

On Thu, 7 Dec 2023 20:19:00 +1030, Qu Wenruo wrote:

> On 2023/12/7 17:50, David Disseldorp wrote:
> > btrfs/282 fails intermittently under some circumstances. This patchset
> > adds dmdelay to make storage latencies more uniform and slightly
> > increases throttled rate tolerances.
>
> My concern using dm_delay is, is the delay per-merged-bio or something else?
>
> If the delay is only per-bio (after merge), then I'm afraid it would not
> be good enough.

The dmdelay device presents itself as a regular block device, so I think
delay_map()->delay_bio() handling comes after any merges.

> The bio plug we use in scrub can have much higher chance to result a
> difference in the scrub speed.
>
> We may want a delay behavior which can take bio size into consideration
> at least.

Should we manipulate it a bit by fiddling with queue/max_sectors_kb and
queue/nomerges?

Thanks, David