Re: [PATCH] btrfs: do not zero f_bavail if we have available space

David Sterba
2020-02-02T17:53:11Z

On Fri, Jan 31, 2020 at 09:31:05AM -0500, Josef Bacik wrote:
> There was some logic added a while ago to clear out f_bavail in statfs()
> if we did not have enough free metadata space to satisfy our global
> reserve. This was incorrect at the time, however didn't really pose a
> problem for normal file systems because we would often allocate chunks
> if we got this low on free metadata space, and thus wouldn't really hit
> this case unless we were actually full.
>
> Fast forward to today and now we are much better about not allocating
> metadata chunks all of the time. Couple this with d792b0f19711 which
> now means we'll easily have a larger global reserve than our free space,
> we are now more likely to trip over this while still having plenty of
> space.
>
> Fix this by skipping this logic if the global rsv's space_info is not
> full. space_info->full is 0 unless we've attempted to allocate a chunk
> for that space_info and that has failed. If this happens then the space
> for the global reserve is definitely sacred and we need to report
> b_avail == 0, but before then we can just use our calculated b_avail.
>
> There are other cases where df isn't quite right, and Qu is addressing
> them in a more holistic way. This simply fixes the users that are
> currently experiencing pain because of this problem.
>
> Fixes: ca8a51b3a979 ("btrfs: statfs: report zero available if metadata are exhausted")
> Reported-by: Martin Steigerwald <martin@lichtvoll.de>
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

Added to 5.6 queue, thanks.