Re: [PATCH] btrfs-progs: do not use async discard for misc/004

[David Sterba <dsterba@suse.cz>]

On Fri, Jun 07, 2024 at 08:00:45PM +0930, Qu Wenruo wrote:
> [BUG]
> There is a long long existing failure in my local VM that with any newer
> kernel (6.x) the test case misc/004 would fail with ENOSPC during
> balance:
> 
>     [TEST]   misc-tests.sh
>     [TEST/misc]   004-shrink-fs
>  failed: /home/adam/btrfs-progs/btrfs balance start -mconvert=single -sconvert=single -f /home/adam/btrfs-progs/tests/mnt
>  test failed for case 004-shrink-fs
>  make: *** [Makefile:547: test-misc] Error 1
> 
> [CAUSE]
> With more testing, it turns out that just before the balance, the
> filesystem still have several empty data block groups.
> 
> The reason is the new default discard=async behavior, as it also changes
> the empty block groups to be async, this leave the empty block groups
> there, resulting no extra space for the convert balance.
> 
> [FIX]
> I do not understand why for loopback block devices we also enable
> discard, but at least disable discard for the test case so that we can
> ensure the empty block groups get cleaned up properly.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Added to devel, thanks.