[PATCHv3 08/10] blk-integrity: remove inappropriate limit checks

[Keith Busch]

On Wed, Sep 11, 2024 at 10:18:46AM +0200, Christoph Hellwig wrote:
> On Tue, Sep 10, 2024 at 10:21:09AM -0600, Keith Busch wrote:
> > I was hoping to not introduce another queue limit for the metadata
> > virt_boundary_mask. We could remove the virt_boundary from the NVMe PCI
> > driver if it supports SGL's and then we're fine. But we're commiting to
> > that data format for all IO even if PRP might have been more efficient.
> > That might be alright, though.
> 
> The real question is if we actually want that.  If we want to take
> fully advantage of the new dma mapping API that Leon is proposing we'd
> need to impose a similar limit.  And a lot of these super tiny SGL
> segments probably aren't very efficient to start with.  Something that
> bounce buffers a page worth of PI tuples might end up beeing more
> efficient in the end.

Yes, a bounce buffer is more efficient for the device side of the
transaction. We have the infrastructure for it when the integrity data
comes from user space addresses, so I suppose we could introduce a "kern"
equivalent.

But currently, instead of many small SGL's stiched together in a single
command, we have the same small SGLs in their own commands. I think this
patch set is a step in the right direction, and doesn't preclude bounce
optimizations.