Re: [PATCH] md: don't account io stat for split bio

[Guoqing Jiang <jgq516@gmail.com>]

On 5/11/21 3:49 AM, Artur Paszkiewicz wrote:
> On 5/10/21 9:46 AM, Guoqing Jiang wrote:
>> On 5/10/21 2:00 PM, Christoph Hellwig wrote:
>>> On Sat, May 08, 2021 at 11:48:15AM +0800, Guoqing Jiang wrote:
>>>> It looks like stack overflow happened for split bio, to fix this,
>>>> let's keep split bio untouched in md_submit_bio.
>>>>
>>>> As a side effect, we need to export bio_chain_endio.
>>> Err, no.  The right answer is to not change ->bi_end_io of bios that
>>> you do not own instead of using a horrible hack to skip accounting for
>>> bios that have no more or less reason to be accounted than others bios.
>> Thanks for the reply. I suppose that md needs to revert current
>> implementation of accounting io stats, then re-implement it.
>>
>> Song and Artur, what are your opinion?
> In the initial version of the io accounting patch the bio was cloned instead
> of just overriding bi_end_io and bi_private. Would this be the right approach?
>
> https://lore.kernel.org/linux-raid/20200601161256.27718-1-artur.paszkiewicz@intel.com/

Maybe we can have different approach for different personality layers.

1. raid1 and raid10 can do the accounting in their own layer since they 
already
     clone bio here.
2. make the initial version handles other personality such as raid0 and 
raid5
     in the md layer.

Also a sysfs node which can enable/disable the accounting could be helpful.

Thanks,
Guoqing