Re: [PATCH v2] dm: Preserve the order of REQ_PREFLUSH writes

[Damien Le Moal <dlemoal@kernel.org>]

On 9/12/25 08:16, Bart Van Assche wrote:
> 
> On 9/11/25 4:03 PM, Damien Le Moal wrote:
>> I suspect it is because this will be handled by the flush machinery during the
>> submit_bio() to the underlying device ?
> 
> Indeed.
> 
>> But if that is the case, why is it a problem with multiple devices ?
>> The same block layer flush machinery will handle that preflush write for all devices.
> The REQ_PREFLUSH semantics require that the REQ_PREFLUSH is submitted to 
> *all* underlying devices before the data that is included in the bio is
> written, even if the data in the bio only affects a single underlying
> device.

You patch would be much better with all this explained in the commit message.
Please add the above explanation in the next version with Mikulas comments
addressed.
Of note is that this seems to apply to all devices, and not just zoned ones.



-- 
Damien Le Moal
Western Digital Research