Re: [PATCH RFC] btrfs: zoned: make auto-reclaim less aggressive

[Josef Bacik <josef@toxicpanda.com>]

On Fri, Feb 11, 2022 at 05:54:02AM -0800, Johannes Thumshirn wrote:
> The current auto-reclaim algorithm starts reclaiming all block-group's
> with a zone_unusable value above a configured threshold. This is causing a
> lot of reclaim IO even if there would be enough free zones on the device.
> 
> Instead of only accounting a block-group's zone_unusable value, also take
> the number of empty zones into account.
> 
> Cc: Josef Bacik <josef@toxicpanda.com>
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> 
> ---
> 
> RFC because I'm a bit unsure about the user interface. Should we use the
> same value / sysfs file for both the number of non-empty zones and the
> number of zone_unusable bytes per block_group or add another knob to fine
> tune?
> 

I want per-space_info thresholds, because for us we want to never relocate
metadata block groups and set a threshold for data.

But I think for this we could have a separate threshold of "don't start
auto-relocate until we are below X threshold for the whole file system" and this
could be the fs wide setting.  Does that make sense?  Thanks,

Josef