Re: [PATCH RFC 3/3] btrfs: space-info: Use per-profile available space in can_overcommit()

[Josef Bacik <josef@toxicpanda.com>]

On 12/25/19 8:39 AM, Qu Wenruo wrote:
> For the following disk layout, can_overcommit() can cause false
> confidence in available space:
> 
>    devid 1 unallocated:	1T
>    devid 2 unallocated:	10T
>    metadata type:	RAID1
> 
> As can_overcommit() simply uses unallocated space with factor to
> calculate the allocatable metadata chunk size.
> 
> can_overcommit() believes we still have 5.5T for metadata chunks, while
> the truth is, we only have 1T available for metadata chunks.
> This can lead to ENOSPC at run_delalloc_range() and cause transaction
> abort.
> 
> Since factor based calculation can't distinguish RAID1/RAID10 and DUP at
> all, we need proper chunk-allocator level awareness to do such estimation.
> 
> Thankfully, we have per-profile available space already calculated, just
> use that facility to avoid such false confidence.
> 
> Reported-by: Marc Lehmann <schmorp@schmorp.de>
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef