[PATCH v6 00/34] iov_iter: Improve page extraction (ref, pin or just list)

[PATCH v6 00/34] iov_iter: Improve page extraction (ref, pin or just list)

[David Howells]

Hi Al, Christoph,

Here are patches clean up some use of READ/WRITE and ITER_SOURCE/DEST,
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.
I've also added a bunch of other conversions and had a tentative stab at
the networking code.

The patches make the following changes:

 (1) Deal with switching from using the iterator data_source to indicate
     the I/O direction to deriving this from other information, eg.:
     IOCB_WRITE, IOMAP_WRITE and the REQ_OP_* number.  This allows
     iov_iter_rw() to be removed eventually.

 (2) Define FOLL_SOURCE_BUF and FOLL_DEST_BUF and pass these into
     iov_iter_get_pages*() to indicate the I/O direction with regards to
     how the buffer described by the iterator is to be used.  This is
     included in the gup_flags passed in with Logan's patches.

     Calls to iov_iter_get_pages*2() are replaced with calls to
     iov_iter_get_pages*() and the former is removed.

 (3) 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.

     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.

 (4) 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.  These are forced to have the same value as the FOLL_* flags so
     they can be passed to the previously mentioned cleanup function.

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

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

 (7) Add a function in netfslib, netfs_extract_user_iter(), to extract a
     UBUF- or IOVEC-type iterator to a page list in a BVEC-type iterator,
     with all the pages suitably ref'd or pinned.

 (8) Add a function in netfslib, netfs_extract_iter_to_sg(), to extract a
     UBUF-, IOVEC-, BVEC-, XARRAY- or KVEC-type iterator to a scatterlist.
     The first two types appropriately ref or pin pages; the latter three
     don't perform any retention, leaving that to the caller.

     Note that I can make use of this in the SCSI and AF_ALG code and
     possibly the networking code, so this might merit being moved to core
     code.

 (9) Make AF_ALG use iov_iter_extract_pages() and possibly go further and
     make it use netfs_extract_iter_to_sg() instead.

(10) Make SCSI vhost use netfs_extract_iter_to_sg().

(11) Make fs/direct-io.c use iov_iter_extract_pages().

(13) Make splice-to-pipe use iov_iter_extract_pages(), but limit the usage
     to a cleanup mode of FOLL_GET.

(13) Make the 9P, FUSE and NFS filesystems use iov_iter_extract_pages().

(14) Make the CIFS filesystem use iterators from the top all the way down
     to the socket on the simple path.  Make it use
     netfs_extract_user_iter() to use an XARRAY-type iterator or to build a
     BVEC-type iterator in the top layers from a UBUF- or IOVEC-type
     iterator and attach the iterator to the operation descriptors.

     netfs_extract_iter_to_sg() is used to build scatterlists for doing
     transport crypto and a function, smb_extract_iter_to_rdma(), is
     provided to build an RDMA SGE list directly from an iterator without
     going via a page list and then a scatter list.

(15) A couple of work-in-progress patches to try and make sk_buff fragments
     record the information needed to clean them up in the lowest two bits
     of the page pointer in the fragment struct.

This leaves:

 (*) Four calls to iov_iter_get_pages() in CEPH.  That will be helped by
     patches to pass an iterator down to the transport layer instead of
     converting to a page list high up and passing that down, but the
     transport layer could do with some massaging so that it doesn't covert
     the iterator to a page list and then the pages individually back to
     iterators to pass to the socket.

 (*) One call to iov_iter_get_pages() each in the networking core, RDS and
     TLS, all related to zero-copy.  TLS seems to do zerocopy-read (or
     maybe decrypt-offload) and should be doing FOLL_PIN, not FOLL_GET for
     user-provided buffers.


Changes:
========
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@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166722777223.2555743.162508599131141451.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166732024173.3186319.18204305072070871546.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166869687556.3723671.10061142538708346995.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166920902005.1461876.2786264600108839814.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/166997419665.9475.15014699817597102032.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/167305160937.1521586.133299343565358971.stgit@warthog.procyon.org.uk/ # v4
Link: https://lore.kernel.org/r/167344725490.2425628.13771289553670112965.stgit@warthog.procyon.org.uk/ # v5

Previous versions of the CIFS patch sets can be found here:
Link: https://lore.kernel.org/r/164311902471.2806745.10187041199819525677.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/164928615045.457102.10607899252434268982.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/165211416682.3154751.17287804906832979514.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/165348876794.2106726.9240233279581920208.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/165364823513.3334034.11209090728654641458.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/166126392703.708021.14465850073772688008.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/166697254399.61150.1256557652599252121.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166732024173.3186319.18204305072070871546.stgit@warthog.procyon.org.uk/ # rfc


---
David Howells (34):
      vfs: Unconditionally set IOCB_WRITE in call_write_iter()
      iov_iter: Use IOCB/IOMAP_WRITE/op_is_write rather than iterator direction
      iov_iter: Pass I/O direction into iov_iter_get_pages*()
      iov_iter: Remove iov_iter_get_pages2/pages_alloc2()
      iov_iter: Change the direction macros into an enum
      iov_iter: Use the direction in the iterator functions
      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
      bio: Rename BIO_NO_PAGE_REF to BIO_PAGE_REFFED and invert the meaning
      mm, block: Make BIO_PAGE_REFFED/PINNED the same as FOLL_GET/PIN numerically
      iov_iter, block: Make bio structs pin pages rather than ref'ing if appropriate
      bio: Fix bio_flagged() so that gcc can better optimise it
      netfs: Add a function to extract a UBUF or IOVEC into a BVEC iterator
      netfs: Add a function to extract an iterator into a scatterlist
      af_alg: Pin pages rather than ref'ing if appropriate
      af_alg: [RFC] Use netfs_extract_iter_to_sg() to create scatterlists
      scsi: [RFC] Use netfs_extract_iter_to_sg()
      dio: Pin pages rather than ref'ing if appropriate
      fuse:  Pin pages rather than ref'ing if appropriate
      vfs: Make splice use iov_iter_extract_pages()
      9p: Pin pages rather than ref'ing if appropriate
      nfs: Pin pages rather than ref'ing if appropriate
      cifs: Implement splice_read to pass down ITER_BVEC not ITER_PIPE
      cifs: Add a function to build an RDMA SGE list from an iterator
      cifs: Add a function to Hash the contents of an iterator
      cifs: Add some helper functions
      cifs: Add a function to read into an iter from a socket
      cifs: Change the I/O paths to use an iterator rather than a page list
      cifs: Build the RDMA SGE list directly from an iterator
      cifs: Remove unused code
      cifs: Fix problem with encrypted RDMA data read
      cifs: DIO to/from KVEC-type iterators should now work
      net: [RFC][WIP] Mark each skb_frags as to how they should be cleaned up
      net: [RFC][WIP] Make __zerocopy_sg_from_iter() correctly pin or leave pages unref'd


 block/bio.c               |   48 +-
 block/blk-map.c           |   26 +-
 block/blk.h               |   25 +
 block/fops.c              |    8 +-
 crypto/af_alg.c           |   57 +-
 crypto/algif_hash.c       |   20 +-
 drivers/net/tun.c         |    2 +-
 drivers/vhost/scsi.c      |   75 +-
 fs/9p/vfs_addr.c          |    2 +-
 fs/affs/file.c            |    4 +-
 fs/ceph/addr.c            |    2 +-
 fs/ceph/file.c            |   16 +-
 fs/cifs/Kconfig           |    1 +
 fs/cifs/cifsencrypt.c     |  172 +++-
 fs/cifs/cifsfs.c          |   12 +-
 fs/cifs/cifsfs.h          |    6 +
 fs/cifs/cifsglob.h        |   66 +-
 fs/cifs/cifsproto.h       |   11 +-
 fs/cifs/cifssmb.c         |   13 +-
 fs/cifs/connect.c         |   16 +
 fs/cifs/file.c            | 1851 +++++++++++++++++--------------------
 fs/cifs/fscache.c         |   22 +-
 fs/cifs/fscache.h         |   10 +-
 fs/cifs/misc.c            |  132 +--
 fs/cifs/smb2ops.c         |  374 ++++----
 fs/cifs/smb2pdu.c         |   45 +-
 fs/cifs/smbdirect.c       |  511 ++++++----
 fs/cifs/smbdirect.h       |    4 +-
 fs/cifs/transport.c       |   57 +-
 fs/dax.c                  |    6 +-
 fs/direct-io.c            |   77 +-
 fs/exfat/inode.c          |    6 +-
 fs/ext2/inode.c           |    2 +-
 fs/f2fs/file.c            |   10 +-
 fs/fat/inode.c            |    4 +-
 fs/fuse/dax.c             |    2 +-
 fs/fuse/dev.c             |   24 +-
 fs/fuse/file.c            |   34 +-
 fs/fuse/fuse_i.h          |    1 +
 fs/hfs/inode.c            |    2 +-
 fs/hfsplus/inode.c        |    2 +-
 fs/iomap/direct-io.c      |    6 +-
 fs/jfs/inode.c            |    2 +-
 fs/netfs/Makefile         |    1 +
 fs/netfs/iterator.c       |  371 ++++++++
 fs/nfs/direct.c           |   32 +-
 fs/nilfs2/inode.c         |    2 +-
 fs/ntfs3/inode.c          |    2 +-
 fs/ocfs2/aops.c           |    2 +-
 fs/orangefs/inode.c       |    2 +-
 fs/reiserfs/inode.c       |    2 +-
 fs/splice.c               |   10 +-
 fs/udf/inode.c            |    2 +-
 include/crypto/if_alg.h   |    7 +-
 include/linux/bio.h       |   23 +-
 include/linux/blk_types.h |    3 +-
 include/linux/fs.h        |   11 +
 include/linux/mm.h        |   32 +-
 include/linux/netfs.h     |    6 +
 include/linux/skbuff.h    |  124 ++-
 include/linux/uio.h       |   83 +-
 io_uring/net.c            |    2 +-
 lib/iov_iter.c            |  428 ++++++++-
 mm/gup.c                  |   47 +
 mm/vmalloc.c              |    1 +
 net/9p/trans_common.c     |    6 +-
 net/9p/trans_common.h     |    3 +-
 net/9p/trans_virtio.c     |   91 +-
 net/bpf/test_run.c        |    2 +-
 net/core/datagram.c       |   23 +-
 net/core/gro.c            |    2 +-
 net/core/skbuff.c         |   16 +-
 net/core/skmsg.c          |    4 +-
 net/ipv4/ip_output.c      |    2 +-
 net/ipv4/tcp.c            |    4 +-
 net/ipv6/esp6.c           |    5 +-
 net/ipv6/ip6_output.c     |    2 +-
 net/packet/af_packet.c    |    2 +-
 net/rds/message.c         |    4 +-
 net/tls/tls_sw.c          |    5 +-
 net/xfrm/xfrm_ipcomp.c    |    2 +-
 81 files changed, 3006 insertions(+), 2126 deletions(-)
 create mode 100644 fs/netfs/iterator.c

[PATCH v6 07/34] iov_iter: Add a function to extract a page list from an iterator

[David Howells]

Add a function, iov_iter_extract_pages(), to extract a list of pages from
an iterator.  The pages may be returned with a reference added or a pin
added or neither, depending on the type of iterator and the direction of
transfer.  The caller should pass FOLL_SOURCE_BUF or FOLL_DEST_BUF as part
of gup_flags to indicate how the iterator contents are to be used.

Add a second function, iov_iter_extract_mode(), to determine how the
cleanup should be done.

There are three cases:

 (1) Transfer *into* an ITER_IOVEC or ITER_UBUF iterator.

     Extracted pages will have pins obtained on them (but not references)
     so that fork() doesn't CoW the pages incorrectly whilst the I/O is in
     progress.

     iov_iter_extract_mode() will return FOLL_PIN for this case.  The
     caller should use something like unpin_user_page() to dispose of the
     page.

 (2) Transfer is *out of* an ITER_IOVEC or ITER_UBUF iterator.

     Extracted pages will have references obtained on them, but not pins.

     iov_iter_extract_mode() will return FOLL_GET.  The caller should use
     something like put_page() for page disposal.

 (3) Any other sort of iterator.

     No refs or pins are obtained on the page, the assumption is made that
     the caller will manage page retention.

     iov_iter_extract_mode() will return 0.  The pages don't need
     additional disposal.

Changes:
========
ver #6)
 - Add back the function to indicate the cleanup mode.
 - Drop the cleanup_mode return arg to iov_iter_extract_pages().
 - Pass FOLL_SOURCE/DEST_BUF in gup_flags.  Check this against the iter
   data_source.

ver #4)
 - Use ITER_SOURCE/DEST instead of WRITE/READ.
 - Allow additional FOLL_* flags, such as FOLL_PCI_P2PDMA to be passed in.

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

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Christoph Hellwig <hch@lst.de>
cc: John Hubbard <jhubbard@nvidia.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org

Link: https://lore.kernel.org/r/Y3zFzdWnWlEJ8X8/@infradead.org/ [1]
Link: https://lore.kernel.org/r/166722777971.2555743.12953624861046741424.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166732025748.3186319.8314014902727092626.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166869689451.3723671.18242195992447653092.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166920903885.1461876.692029808682876184.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/166997421646.9475.14837976344157464997.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/167305163883.1521586.10777155475378874823.stgit@warthog.procyon.org.uk/ # v4
Link: https://lore.kernel.org/r/167344728530.2425628.9613910866466387722.stgit@warthog.procyon.org.uk/ # v5
---

 include/linux/uio.h |   28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 18b64068cc6d..38607c82e0cc 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -373,4 +373,32 @@ static inline void iov_iter_ubuf(struct iov_iter *i, enum iter_dir direction,
 	};
 }
 
+ssize_t iov_iter_extract_pages(struct iov_iter *i, struct page ***pages,
+			       size_t maxsize, unsigned int maxpages,
+			       unsigned int gup_flags, size_t *offset0);
+
+/**
+ * iov_iter_extract_mode - Indicate how pages from the iterator will be retained
+ * @iter: The iterator
+ * @gup_flags: How the iterator is to be used (FOLL_SOURCE/DEST_BUF)
+ *
+ * Examine the iterator and the gup_flags and indicate by returning FOLL_PIN,
+ * FOLL_GET or 0 as to how, if at all, pages extracted from the iterator will
+ * be retained by the extraction function.
+ *
+ * FOLL_GET indicates that the pages will have a reference taken on them that
+ * the caller must put.  This can be done for DMA/async DIO write from a page.
+ *
+ * FOLL_PIN indicates that the pages will have a pin placed in them that the
+ * caller must unpin.  This is must be done for DMA/async DIO read to a page to
+ * avoid CoW problems in fork.
+ *
+ * 0 indicates that no measures are taken and that it's up to the caller to
+ * retain the pages.
+ */
+#define iov_iter_extract_mode(iter, gup_flags) \
+	(user_backed_iter(iter) ?				\
+	 (gup_flags & FOLL_BUF_MASK) == FOLL_SOURCE_BUF ?	\
+	 FOLL_GET : FOLL_PIN : 0)
+
 #endif

Re: [PATCH v6 00/34] iov_iter: Improve page extraction (ref, pin or just list)

[Christoph Hellwig]

First off the liver comment:  can we cut down things for a first
round?  Maybe just convert everything using the bio based helpers
and then chunk it up?  Reviewing 34 patches across a dozen subsystems
isn't going to be easy and it will be hard to come up with a final
positive conclusion.

Re: [PATCH v6 07/34] iov_iter: Add a function to extract a page list from an iterator

[Christoph Hellwig]

> Changes:
> ========
> ver #6)
>  - Add back the function to indicate the cleanup mode.
>  - Drop the cleanup_mode return arg to iov_iter_extract_pages().
>  - Pass FOLL_SOURCE/DEST_BUF in gup_flags.  Check this against the iter
>    data_source.

FYI, the changelog goes after the --- so that it doesn't get added
to the git history.

> Link: https://lore.kernel.org/r/166732025748.3186319.8314014902727092626.stgit@warthog.procyon.org.uk/ # rfc
> Link: https://lore.kernel.org/r/166869689451.3723671.18242195992447653092.stgit@warthog.procyon.org.uk/ # rfc
> Link: https://lore.kernel.org/r/166920903885.1461876.692029808682876184.stgit@warthog.procyon.org.uk/ # v2
> Link: https://lore.kernel.org/r/166997421646.9475.14837976344157464997.stgit@warthog.procyon.org.uk/ # v3
> Link: https://lore.kernel.org/r/167305163883.1521586.10777155475378874823.stgit@warthog.procyon.org.uk/ # v4
> Link: https://lore.kernel.org/r/167344728530.2425628.9613910866466387722.stgit@warthog.procyon.org.uk/ # v5

And all these links aren't exactly useful.  This fairly trivial commit
is going to look like a hot mess in git.

> +ssize_t iov_iter_extract_pages(struct iov_iter *i, struct page ***pages,
> +			       size_t maxsize, unsigned int maxpages,
> +			       unsigned int gup_flags, size_t *offset0);

This function isn't actually added in the current patch.

> +#define iov_iter_extract_mode(iter, gup_flags) \
> +	(user_backed_iter(iter) ?				\
> +	 (gup_flags & FOLL_BUF_MASK) == FOLL_SOURCE_BUF ?	\
> +	 FOLL_GET : FOLL_PIN : 0)

And inline function would be nice here.  I guess that would require
moving the FULL flags into mm_types.h, though.

Re: [PATCH v6 07/34] iov_iter: Add a function to extract a page list from an iterator

[David Howells]

Christoph Hellwig <hch@infradead.org> wrote:

> > +ssize_t iov_iter_extract_pages(struct iov_iter *i, struct page ***pages,
> > +			       size_t maxsize, unsigned int maxpages,
> > +			       unsigned int gup_flags, size_t *offset0);
> 
> This function isn't actually added in the current patch.

Oh...  It ended up in the wrong patch.

> > +#define iov_iter_extract_mode(iter, gup_flags) \
> > +	(user_backed_iter(iter) ?				\
> > +	 (gup_flags & FOLL_BUF_MASK) == FOLL_SOURCE_BUF ?	\
> > +	 FOLL_GET : FOLL_PIN : 0)
> 
> And inline function would be nice here.  I guess that would require
> moving the FULL flags into mm_types.h, though.

Yeah, the movement of FOLL_* flags is queued in a patch in akpm's tree.

David