Re: [dm-devel] [PATCH v3 13/16] Make generic_make_request handle arbitrarily large bios

[Alasdair G Kergon <agk redhat com>]

On Fri, May 25, 2012 at 01:25:36PM -0700, Kent Overstreet wrote:
> But this approach becomes unwieldy and eventually breaks down with
> stacked devices and devices with dynamic limits, and it adds a lot of
> complexity. If the block layer could split bios as needed, we could

Complexity - yes - but if people didn't observe a genuine benefit, why
did they go to the trouble of writing this and getting it included?

> eliminate a lot of complexity elsewhere - particularly in stacked
> drivers. 

> Code that creates bios can then create whatever size bios are
> convenient, and more importantly stacked drivers don't have to deal with
> both their own bio size limitations and the limitations of the
> (potentially multiple) devices underneath them.

A theoretical argument.  Perhaps it's the right assessment of this
issue.  Perhaps it's not.  Or perhaps it depends on the use-case.

I made a theoretical argument from a different point of view in my last email.

I think a body of *empirical* evidence should provide the justification
for this particular change, and until such evidence is forthcoming we
should keep the status quo.

Alasdair