Merge tag 'large-folio-writes' of git://git.infradead.org/users/willy/pagecache into...

Create large folios in iomap buffered write path

Commit ebb7fb1557b1 limited the length of ioend chains to 4096 entries
to improve worst-case latency.  Unfortunately, this had the effect of
limiting the performance of:

fio -name write-bandwidth -rw=write -bs=1024Ki -size=32Gi -runtime=30 \
        -iodepth 1 -ioengine sync -zero_buffers=1 -direct=0 -end_fsync=1 \
        -numjobs=4 -directory=/mnt/test

https://lore.kernel.org/linux-xfs/20230508172406.1CF3.409509F4@e16-tech.com/

The problem ends up being lock contention on the i_pages spinlock as we
clear the writeback bit on each folio (and propagate that up through
the tree).  By using larger folios, we decrease the number of folios
to be processed by a factor of 256 for this benchmark, eliminating the
lock contention.

Creating large folios in the buffered write path is also the right
thing to do.  It's a project that has been on the back burner for years,
it just hasn't been important enough to do before now.

* tag 'large-folio-writes' of git://git.infradead.org/users/willy/pagecache:
  iomap: Copy larger chunks from userspace
  iomap: Create large folios in the buffered write path
  filemap: Allow __filemap_get_folio to allocate large folios
  filemap: Add fgf_t typedef
  iomap: Remove unnecessary test from iomap_release_folio()
  doc: Correct the description of ->release_folio
  iomap: Remove large folio handling in iomap_invalidate_folio()
  iov_iter: Add copy_folio_from_iter_atomic()
  iov_iter: Handle compound highmem pages in copy_page_from_iter_atomic()
  iov_iter: Map the page later in copy_page_from_iter_atomic()

[djwong: yay amortizations!]
Signed-off-by: Darrick J. Wong <djwong@kernel.org>