[PATCH for-next v4 3/4] block: add helper to map bvec iterator for passthrough

[Jens Axboe]

On 9/6/22 12:51 AM, Christoph Hellwig wrote:
> On Tue, Sep 06, 2022 at 12:03:29PM +0530, Kanchan Joshi wrote:
>>> This context looks weird?  That bio_alloc_bioset should not be there,
>>> as biosets are only used for file system I/O, which this is not.
>>
>> if you think it's a deal-breaker, maybe I can add a new bioset in nvme and
>> pass that as argument to this helper. Would you prefer that over the
>> current approach.
> 
> The whole point is that biosets exist to allow for forward progress
> guarantees required for file system I/O.  For passthrough I/O
> bio_kmalloc is perfectly fine and much simpler.  Adding yet another
> bio_set just makes things even worse.

It's a performance concern too, efficiency is much worse by using
kmalloc+kfree for passthrough. You don't get bio caching that way.

-- 
Jens Axboe