Re: [PATCH] btrfs: mkfs: Make no-holes as default mkfs incompat features

[Anand Jain <anand.jain@oracle.com>]

On 12/11/19 9:01 AM, Qu Wenruo wrote:
> 
> 
> On 2019/11/12 上午2:02, David Sterba wrote:
>> On Mon, Nov 11, 2019 at 02:50:04PM +0800, Qu Wenruo wrote:
>>> No-holes feature could save 53 bytes for each hole we have, and it
>>> provides a pretty good workaround to prevent btrfs check from reporting
>>> non-contiguous file extent holes for mixed direct/buffered IO.
>>>
>>> The latter feature is more helpful for developers for handle log-writes
>>> based test cases.
>>
>> Thanks. The plan to make no-holes default has been there for some time
>> already. What it needs is a full round of testing and validation before
>> making it default. And as defaults change rarely, I'd like to add
>> free-space-tree as mkfs default as well, there's enough demand for that
>> and we want to start deprecating v1 in the future.
>>
>> I have in my near-top todo list to do that, with the following
>> checklist:
>>
>> - run fstests with various features together + the new default
>>    - release build
>>    - debugging build with UBSAN, KASAN and additional useful debugging
>>      tools
> Already running with no_holes for several previous releases.
> 
> Not to mention new btrfs specific log-writes test cases are all already
> using this feature  to avoid btrfs check failure.
> 
> So I think this part should be OK.
> 
>> - run stress tests + the new feature
> 
> Any extra suggestions for the stress test tool?
> 
> Despite that, extra 24x7 host may be needed for this test.
> 

   To keep the ball rolling I can run stress tests part here,
   yep need extra suggestions on the stress test tools.

Thanks, Anand

>> - check that the documentation covers the change
>>    - mkfs.btrfs help string
>>    - manual page of mkfs.btrfs: benefits, pros/cons, conversion to/from
>>      the feature (if applicable), with example commands (if applicable)
>>    - wiki documentation update
> 
> Forgot this part.
> I'll add this info in next update.
> 
> Thanks,
> Qu
>> - verify that all commonly used tools work with it (image, check, tune)
>>
>> For free-space-tree specifically, there's
>> https://github.com/kdave/drafts/blob/master/btrfs/progs-fst-default.txt
>>
>> I don't have objections to the patch, that's the easy part. The above is
>> non-coding work and is namely making sure that the usecase and usability
>> is good, or with known documented quirks.
>>
>> Making it default in progs release 5.4 is IMO doable, there are probably
>> 2-3 weeks before the release, but this task needs one or more persons
>> willing to do the above.
>>
>