[dm-devel] [PATCH 1/5] block: Make generic_make_request handle arbitrary sized bios

[Christoph Hellwig]

> +	q->bio_split = bioset_create(4, 0);
> +	if (!q->bio_split)
> +		goto fail_id;

How did we arrive at a mempool size of 4 to make sure we can always make
progress with arbitrarily sized bios?  Shouldn't we document the design
decision somewhere?

> +static struct bio *blk_bio_discard_split(struct request_queue *q,
> +					 struct bio *bio,
> +					 struct bio_set *bs)
> +{

One fallout of this should be that it would allows us to impement
a range UNMAP/TRIP much more easily, which would help dramatically
with TRIM performance!