On Mon, Jul 02, 2018 at 10:49:46AM +0300, Nikolay Borisov wrote:
> On 2.07.2018 10:44, Ethan Lien wrote:
> > We use customized, nodesize batch value to update dirty_metadata_bytes.
> > We should also use batch version of compare function or we will easily
> > goto fast path and get false result from percpu_counter_compare().
> >
> > Signed-off-by: Ethan Lien <ethanlien@xxxxxxxxxxxx>
>
> Reviewed-by: Nikolay Borisov <nborisov@xxxxxxxx>
>
> Also this needs the following tag:
>
> Fixes: e2d845211eda ("Btrfs: use percpu counter for dirty metadata count")
I'll add the tags, thanks.
2939 fs_info->dirty_metadata_batch = nodesize * (1 + ilog2(nr_cpu_ids));
What a commit, sigh. Arbitrary constants without any explanation. I
don't quite understand why the ilog2(nr_cpui_ids) was chosen. If cpus
are onlined/offlined there's no adjustment. I'd think that there should
be some amount of data that are supposed to be dirtied per-cpu and this
value is independent of the number of cpus. That the online/offline
status is abstracted by the percpu API. I don't have time to study that
too deeply, but this is something that needs to be revisited.
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