Re: [PATCH 1/5] block: new sector copy api

[Keith Busch <kbusch@kernel.org>]

On Sun, May 25, 2025 at 10:18:27PM -0700, Christoph Hellwig wrote:
> Well, I'd expect most uses cases of things like GC to use the "fallback"
> for now - because copy isn't actually that often supported, and when it
> is performance might not be good enough.  So we'll need to optimize
> for both cases.  Maybe a fallback code is useful, but I'd leave the
> buffer management for it to the caller so that it can reuse them.  Or
> maybe don't bother given how trivial the code is anyway.  The use case
> for common code would be strong if it refactored existing code and
> showed that existing callers actually have enough common logic that
> it's worth the effort.

Just fyi, the initial user I was planning to target with the block
layer's copy fallback isn't in kernel yet. Just an RFC at this moment on
btrfs:

  https://lore.kernel.org/linux-btrfs/20250515163641.3449017-10-maharmstone@fb.com/

The blk-lib function could easily replace that patch's "do_copy()"
without to much refactoring on the btrfs side.