Re: [PATCH] btrfs: Test that qgroup counts are valid after snapshot creation

[Mark Fasheh <mfasheh@suse.de>]

On Fri, Apr 22, 2016 at 08:26:33AM +0800, Qu Wenruo wrote:
> 
> 
> Mark Fasheh wrote on 2016/04/21 16:53 -0700:
> >Thank you for the review, comments are below.
> >
> >On Wed, Apr 20, 2016 at 09:48:54AM +0900, Satoru Takeuchi wrote:
> >>On 2016/04/20 7:25, Mark Fasheh wrote:
> >>>+# Force a small leaf size to make it easier to blow out our root
> >>>+# subvolume tree
> >>>+_scratch_mkfs "--nodesize 16384"
> >>
> >>nodesize 16384 is the default value. Do you
> >>intend other value, for example 4096?
> >
> >"future proofing" I suppose - if we up the default, the for loop below may
> >not create a level 1 tree.
> >
> >If we force it smaller than 16K I believe that may mean we can't run this
> >test on some kernels with page size larger than the typical 4k.
> >	--Mark
> >
> >
> >--
> >Mark Fasheh
> >
> >
> 
> Sorry for the late reply.
> 
> Unfortunately, for system with 64K page size, it will fail(mount and
> mkfs) if we use 16K nodesize.
> 
> IIRC, like some other btrfs qgroup test case, we use 64K nodesize as
> the safest nodesize.
> 
> And for level 1 tree create, the idea is to use inline file extents
> to rapidly create level 1 tree.
> 
> 16 4K files should create a level 1 tree.
> Although in this case, max_inline=4096 would be added to mount
> option though.

That all sounds good, thanks. The only thing about filling it completely
with inline extents though is that we should be exercising qgroups a little
harder. But maybe we can blow out the tree with inline extents and then add
some actual data extents after that.
	--Mark

--
Mark Fasheh