btrfs: use kvmalloc() for stripe buffer of scrub_stripe

Currently we're using scrub_stripe::folios[] to store all contents of a
stripe.

This means we need all the extra work to handle things like sub-page
cases, and also require larger folios to handle bs > ps cases.

On the other hand, it's not hard to allocate a 64K large folio to cover
the full stripe, getting rid of the cross-page handling.

Furthermore, even if that large folio allocation failed, we can still
use vmalloc() to allocate a virtually contiguous space and still get rid
of cross-page handling.

This patch will go with kvmalloc() to allocate 64K of memory for
the stripe buffer, thus getting rid of all the complex cross-page
handling.

The following aspects can be greatly simplified:

- Checksum verification for both data and metadata
  No more per-page iteration, all in one go.

- RAID56 data caching
  Just copy the buffer into the RAID56 pages.

- No more kaddr/paddr grabbing
  For most cases the virtual address is enough for csum calculation and
  io submission.

- Bio assembly
  There is already the helper bio_add_vmalloc() to queue vmallocated
  memory into a bio.

Although it means we have something else to be concerned about:

- Bio assembly
  If the memory is vmallocated, we need to use bio_add_vmalloc()
  Otherwise use the existing bio_add_page().

- Read endio
  For vmallocated memory, we need to call
  invalidate_kernel_vmap_range().

- Scrub bbio bvec size
  Since scrub_stripe::buffer is kvmallocated, we also need to enlarge
  the scrub bbio, to be able to handle the worst case, where all 64KiB is
  allocated by discontiguous 4K physical pages.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

0 files changed, 0 insertions, 0 deletions