Re: remove a few uses of ->queuedata

[Christoph Hellwig]

On Fri, May 08, 2020 at 11:04:45AM -0700, Dan Williams wrote:
> On Fri, May 8, 2020 at 9:16 AM Christoph Hellwig <hch@xxxxxx> wrote:
> >
> > Hi all,
> >
> > various bio based drivers use queue->queuedata despite already having
> > set up disk->private_data, which can be used just as easily.  This
> > series cleans them up to only use a single private data pointer.
> 
> ...but isn't the queue pretty much guaranteed to be cache hot and the
> gendisk cache cold? I'm not immediately seeing what else needs the
> gendisk in the I/O path. Is there another motivation I'm missing?

->private_data is right next to the ->queue pointer, pat0 and part_tbl
which are all used in the I/O submission path (generic_make_request /
generic_make_request_checks).  This is mostly a prep cleanup patch to
also remove the pointless queue argument from ->make_request - then
->queue is an extra dereference and extra churn.