[PATCH v7 0/8] iov_iter: Improve page extraction (ref, pin or just list)
From: David Howells
Date: Fri Jan 20 2023 - 12:56:52 EST
Hi Al, Christoph,
Here are patches to provide support for extracting pages from an iov_iter
and a patch to use the primary extraction function 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 and the I/O direction.
Add a function, iov_iter_extract_mode() that will indicate from the
iterator type and the I/O direction how the cleanup is to be
performed, returning FOLL_GET, 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_GET and FOLL_PIN down so that they're at bits 0 and 1
and coincident with BIO_PAGE_REFFED and BIO_PAGE_PINNED. 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.
Changes:
========
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.
I've pushed the patches (excluding the two WIP networking patches) here
also:
https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=iov-extract
David
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
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: Rename BIO_NO_PAGE_REF to BIO_PAGE_REFFED and invert the
meaning
block: Add BIO_PAGE_PINNED
block: Make bio structs pin pages rather than ref'ing if appropriate
block: Fix bio_flagged() so that gcc can better optimise it
mm: Renumber FOLL_GET and FOLL_PIN down
block/bio.c | 43 ++--
block/blk-map.c | 26 +--
block/blk.h | 29 +++
fs/iomap/direct-io.c | 1 -
include/linux/bio.h | 5 +-
include/linux/blk_types.h | 3 +-
include/linux/mm.h | 17 +-
include/linux/uio.h | 35 ++-
lib/iov_iter.c | 438 +++++++++++++++++++++++++++++++++++++-
mm/gup.c | 22 ++
10 files changed, 571 insertions(+), 48 deletions(-)