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[dm-devel] Re: [PATCH RFC 0/4] use scatter lists for all block pc requests and simplify hw handlers



On Tue, Jun 07 2005, James Bottomley wrote:
> On Tue, 2005-06-07 at 23:08 +1000, Douglas Gilbert wrote:
> > I don't think it is important and I'm not aware of any
> > real world applications that are using it. Naturally,
> > I will find out if that is actually true after it
> > gets removed.
> 
> Heh, true.  OK, let's do this: I'll remove it from the sg driver and
> make sg use the do_command (or it's successor) interface.  If an actual
> user for the iovecs does turn up, I'll add it to the block layer (it's a
> fairly well understood multi-bio request setup) and make sg and also the
> block layer SG_IO use it.

Why multi-bio? No one should ever have to build a request with multiple
bio's in one go, that's pointless. The only reason multi-bio requests
exist is because of the file systems not submitting big extents in one
submission. The whole io path would be faster and simpler were it not
for multi-bio requests :-)

A single bio can contain just as much data.

-- 
Jens Axboe


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