Re: [PATCH v3] btrfs: should block unused block groups deletion work when allocating data space

["Holger Hoffstätte" <holger@applied-asynchrony.com>]

On 09/12/16 09:38, Wang Xiaoguang wrote:
<snip>
>> Actually even that is not true; both patches seem to be wrong in subtle
>> ways. Naohiro's patch seems to prevent the deletion during balance, whereas
>> yours prevents the cleaner from kicking in.
> Indeed in my patch, I just change "struct mutex delete_unused_bgs_mutex"
> to "struct rw_semaphore bg_delete_sem", and try to get bg_delete_sem when
> we allocate data space, so this patch should work as before :)
> 
>>
>> As a simple reproducer you can convert from -mdup to -msingle (to create
>> bloat) and then balance with -musage=10. Depending on which of the two
>> patches are applied, you end with bloat that only grows and never shrinks,
>> or bloat that ends up in mixed state (dup and single).
> Can you give me a simple test script to reproduce your problem.
> (I can write it myself, but I'm afraid I may misunderstand you :) )

I don't have a script and no time this week to play with this.
Just create an fs with dup metadata, balance -mconvert=single and then
back with -mconvert=dup. That's all I tried.

Holger