[PATCH v8 00/10] iov_iter: Improve page extraction (pin or just list)

[David Howells]

Hi Al, Christoph,

Here are patches to provide support for extracting pages from an iov_iter
and to use this in the extraction functions in the block layer bio code.

The patches make the following changes:

 (1) Add a function, iov_iter_extract_pages() to replace
     iov_iter_get_pages*() that gets refs, pins or just lists the pages as
     appropriate to the iterator type.

     Add a function, iov_iter_extract_mode() that will indicate from the
     iterator type how the cleanup is to be performed, returning FOLL_PIN
     or 0.

 (2) Add a function, folio_put_unpin(), and a wrapper, page_put_unpin(),
     that take a page and the return from iov_iter_extract_mode() and do
     the right thing to clean up the page.

 (3) Make the bio struct carry a pair of flags to indicate the cleanup
     mode.  BIO_NO_PAGE_REF is replaced with BIO_PAGE_REFFED (equivalent to
     FOLL_GET) and BIO_PAGE_PINNED (equivalent to BIO_PAGE_PINNED) is
     added.

 (4) Add a function, bio_release_page(), to release a page appropriately to
     the cleanup mode indicated by the BIO_PAGE_* flags.

 (5) Make the iter-to-bio code use iov_iter_extract_pages() to retain the
     pages appropriately and clean them up later.

 (6) Fix bio_flagged() so that it doesn't prevent a gcc optimisation.

 (7) Renumber FOLL_PIN and FOLL_GET down so that they're at bits 0 and 1
     and coincident with BIO_PAGE_PINNED and BIO_PAGE_REFFED.  The compiler
     can then optimise on that.  Also, it's probably going to be necessary
     to embed these in the page pointer in sk_buff fragments.  This patch
     can go independently through the mm tree.

I've pushed the patches here also:

	https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=iov-extract

David

Changes:
========
ver #8)
 - Import Christoph Hellwig's changes.
   - Split the conversion-to-extraction patch.
   - Drop the extract_flags arg from iov_iter_extract_mode().
   - Don't default bios to BIO_PAGE_REFFED, but set explicitly.
 - Switch FOLL_PIN and FOLL_GET when renumbering so PIN is at bit 0.
 - Switch BIO_PAGE_PINNED and BIO_PAGE_REFFED so PINNED is at bit 0.
 - We should always be using FOLL_PIN (not FOLL_GET) for DIO, so adjust the
   patches for that.

ver #7)
 - For now, drop the parts to pass the I/O direction to iov_iter_*pages*()
   as it turned out to be a lot more complicated, with places not setting
   IOCB_WRITE when they should, for example.
 - Drop all the patches that changed things other then the block layer's
   bio handling.  The netfslib and cifs changes can go into a separate
   patchset.
 - Add support for extracting pages from KVEC-type iterators.
 - When extracting from BVEC/KVEC, skip over empty vecs at the front.

ver #6)
 - Fix write() syscall and co. not setting IOCB_WRITE.
 - Added iocb_is_read() and iocb_is_write() to check IOCB_WRITE.
 - Use op_is_write() in bio_copy_user_iov().
 - Drop the iterator direction checks from smbd_recv().
 - Define FOLL_SOURCE_BUF and FOLL_DEST_BUF and pass them in as part of
   gup_flags to iov_iter_get/extract_pages*().
 - Replace iov_iter_get_pages*2() with iov_iter_get_pages*() and remove.
 - Add back the function to indicate the cleanup mode.
 - Drop the cleanup_mode return arg to iov_iter_extract_pages().
 - Provide a helper to clean up a page.
 - Renumbered FOLL_GET and FOLL_PIN and made BIO_PAGE_REFFED/PINNED have
   the same numerical values, enforced with an assertion.
 - Converted AF_ALG, SCSI vhost, generic DIO, FUSE, splice to pipe, 9P and
   NFS.
 - Added in the patches to make CIFS do top-to-bottom iterators and use
   various of the added extraction functions.
 - Added a pair of work-in-progess patches to make sk_buff fragments store
   FOLL_GET and FOLL_PIN.

ver #5)
 - Replace BIO_NO_PAGE_REF with BIO_PAGE_REFFED and split into own patch.
 - Transcribe FOLL_GET/PIN into BIO_PAGE_REFFED/PINNED flags.
 - Add patch to allow bio_flagged() to be combined by gcc.

ver #4)
 - Drop the patch to move the FOLL_* flags to linux/mm_types.h as they're
   no longer referenced by linux/uio.h.
 - Add ITER_SOURCE/DEST cleanup patches.
 - Make iov_iter/netfslib iter extraction patches use ITER_SOURCE/DEST.
 - Allow additional gup_flags to be passed into iov_iter_extract_pages().
 - Add struct bio patch.

ver #3)
 - Switch to using EXPORT_SYMBOL_GPL to prevent indirect 3rd-party access
   to get/pin_user_pages_fast()[1].

ver #2)
 - Rolled the extraction cleanup mode query function into the extraction
   function, returning the indication through the argument list.
 - Fixed patch 4 (extract to scatterlist) to actually use the new
   extraction API.

Link: https://lore.kernel.org/r/Y3zFzdWnWlEJ8X8/@infradead.org/ [1]
Link: https://lore.kernel.org/r/166697254399.61150.1256557652599252121.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc
Link: https://lore.kernel.org/r/166722777223.2555743.162508599131141451.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc
Link: https://lore.kernel.org/r/166732024173.3186319.18204305072070871546.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc
Link: https://lore.kernel.org/r/166869687556.3723671.10061142538708346995.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc
Link: https://lore.kernel.org/r/166920902005.1461876.2786264600108839814.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v2
Link: https://lore.kernel.org/r/166997419665.9475.15014699817597102032.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v3
Link: https://lore.kernel.org/r/167305160937.1521586.133299343565358971.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v4
Link: https://lore.kernel.org/r/167344725490.2425628.13771289553670112965.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v5
Link: https://lore.kernel.org/r/167391047703.2311931.8115712773222260073.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v6
Link: https://lore.kernel.org/r/20230120175556.3556978-1-dhowells@xxxxxxxxxx/ # v7

Christoph Hellwig (2):
  iomap: don't get an reference on ZERO_PAGE for direct I/O block
    zeroing
  block: Rename BIO_NO_PAGE_REF to BIO_PAGE_REFFED and invert the
    meaning

David Howells (8):
  iov_iter: Define flags to qualify page extraction.
  iov_iter: Add a function to extract a page list from an iterator
  mm: Provide a helper to drop a pin/ref on a page
  block: Fix bio_flagged() so that gcc can better optimise it
  block: Switch to pinning pages.
  block: Convert bio_iov_iter_get_pages to use iov_iter_extract_pages
  block: convert bio_map_user_iov to use iov_iter_extract_pages
  mm: Renumber FOLL_PIN and FOLL_GET down

 block/bio.c               |  33 ++--
 block/blk-map.c           |  25 ++-
 block/blk.h               |  28 ++++
 fs/direct-io.c            |   2 +
 fs/iomap/direct-io.c      |   1 -
 include/linux/bio.h       |   5 +-
 include/linux/blk_types.h |   3 +-
 include/linux/mm.h        |  35 ++--
 include/linux/uio.h       |  29 +++-
 lib/iov_iter.c            | 334 +++++++++++++++++++++++++++++++++++++-
 mm/gup.c                  |  22 +++
 11 files changed, 461 insertions(+), 56 deletions(-)