[RFC PATCH v2 00/48] splice, net: Replace sendpage with sendmsg(MSG_SPLICE_PAGES)

David Howells
2023-03-29T14:16:30Z

Hi Willy, Dave, et al.,

[NOTE! This patchset is a work in progress and some modules will not
compile with it.]

I've been looking at how to make pipes handle the splicing in of multipage
folios and also looking to see if I could implement a suggestion from Willy
that pipe_buffers could perhaps hold a list of pages (which could make
splicing simpler - an entire splice segment would go in a single
pipe_buffer).

There are a couple of issues here:

(1) Gifting/stealing a multipage folio is really tricky. I think that if
a multipage folio if gifted, the gift flag should be quietly dropped.
Userspace has no control over what splice() and vmsplice() will see in
the pagecache.

(2) The sendpage op expects to be given a single page and various network
protocols just attach that to a socket buffer.

This patchset aims to deal with the second by removing the ->sendpage()
operation and replacing it with sendmsg() and a new internal flag
MSG_SPLICE_PAGES. As sendmsg() takes an I/O iterator, this also affords
the opportunity to pass a slew of pages in one go, rather than one at a
time.

If MSG_SPLICE_PAGES is set, the protocol sendmsg() instance will attempt to
splice the pages out of the buffer, copying into individual fragments those
that it can't (e.g. because they belong to the slab).

The patchset consists of the following parts:

(1) A couple of fixes.

(2) Add an iterator-of-iterators (ITER_ITERLIST). This allows a network
filesystem, say, to glue together buffers described by a number of
different iterators. Sunrpc, for example, can use it to assemble a
message consisting of a couple of headers (KVECs), a body (BVEC) and a
trailer (KVEC). It has very limited application, however, as such
iterators cannot be copied trivially by "*iter1 = *iter2;".

(3) Define the MSG_SPLICE_PAGES flag.

(4) The page_frag_alloc_align() allocator is overhauled:

(a) Split it out from mm/page_alloc.c into its own file,
mm/page_frag_alloc.c.

(b) Make it use multipage folios rather than compound pages.

(c) Give it per-cpu buckets to allocate from so no locking is
required.

(d) The netdev_alloc_cache and the napi fragment cache are then cast
in terms of this and some private allocators are removed.

I'm not sure that the existing allocator is 100% multithread safe.

(5) Implement MSG_SPLICE_PAGES support in TCP.

(6) Make MSG_SPLICE_PAGES copy unspliceable pages (eg. slab pages).

(7) Make do_tcp_sendpages() just wrap sendmsg() and then fold it in to its
various callers.

(8) Implement MSG_SPLICE_PAGES support in IP and make udp_sendpage() just
a wrapper around sendmsg().

(9) Make IP/UDP copy unspliceable pages.

(10) Implement MSG_SPLICE_PAGES support in AF_UNIX.

(11) Make AF_UNIX copy unspliceable pages.

(12) Make AF_ALG use netfs_extract_iter_to_sg().

(13) Make AF_ALG implement MSG_SPLICE_PAGES and make af_alg_sendpage() just
a wrapper around sendmsg().

(14) Make AF_ALG/hash implement MSG_SPLICE_PAGES.

(15) Rename pipe_to_sendpage() to pipe_to_sendmsg() and make it a wrapper
around sendmsg().

(16) Replace splice_to_socket() with an implementation that doesn't use
splice_from_pipe() to push one page at a time, but rather something
that splices up to 16 pages at once. This absorbs pipe_to_sendmsg().

(17) Remove sendpage file operation.

(18) Convert siw, ceph, iscsi and tcp_bpf to use sendmsg() instead of
tcp_sendpage().

(19) Make skb_send_sock() use sendmsg().

(20) Convert ceph, rds, dlm, sunrpc, nvme, kcm, smc, ocfs2 and drbd to use
sendmsg().

(21) Make sunrpc use an iterator-of-iterators to pass through a combination
of iterators that cover the marker, header, body and trailer of a
message in a single sendmsg.

(22) Make sunrpc delegate copying of unspliceable pages to TCP, so that it
can stitch together three ITER_KVECs and an ITER_BVEC into a single
ITER_ITERLIST.

(23) Make drbd delegate copying of slab pages to TCP and pass an entire
bio's bvec to sendmsg at a time. Delegate copying of unspliceable
pages to TCP.

(24) Remove the sendpage socket operation.

This leaves the implementation of MSG_SPLICE_PAGES in AF_KCM, AF_TLS and
Chelsio-TLS which I'm going to need help with. I've killed off all uses of
kernel_sendpage() and all uses of sendpage_ok() outside of the protocols.

I have tested AF_UNIX splicing - which, surprisingly, seems nearly twice as
fast - TCP splicing, the siw driver (softIWarp RDMA with nfs and cifs),
sunrpc (with nfsd) and UDP (using a patched rxrpc).

I've pushed the patches here also:

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

David

Changes
=======
ver #2)
- Overhauled the page_frag_alloc() allocator: large folios and per-cpu.
- Got rid of my own zerocopy allocator.
- Use iov_iter_extract_pages() rather poking in iter->bvec.
- Made page splicing fall back to page copying on a page-by-page basis.
- Made splice_to_socket() pass 16 pipe buffers at a time.
- Made AF_ALG/hash use finup/digest where possible in sendmsg.
- Added an iterator-of-iterators, ITER_ITERLIST.
- Made sunrpc use the iterator-of-iterators.
- Converted more drivers.

Link: https://lore.kernel.org/r/20230316152618.711970-1-dhowells@redhat.com/ # v1

David Howells (48):
netfs: Fix netfs_extract_iter_to_sg() for ITER_UBUF/IOVEC
iov_iter: Remove last_offset member
iov_iter: Add an iterator-of-iterators
net: Declare MSG_SPLICE_PAGES internal sendmsg() flag
mm: Move the page fragment allocator from page_alloc.c into its own
file
mm: Make the page_frag_cache allocator use multipage folios
mm: Make the page_frag_cache allocator use per-cpu
tcp: Support MSG_SPLICE_PAGES
tcp: Make sendmsg(MSG_SPLICE_PAGES) copy unspliceable data
tcp: Convert do_tcp_sendpages() to use MSG_SPLICE_PAGES
tcp_bpf: Inline do_tcp_sendpages as it's now a wrapper around
tcp_sendmsg
espintcp: Inline do_tcp_sendpages()
tls: Inline do_tcp_sendpages()
siw: Inline do_tcp_sendpages()
tcp: Fold do_tcp_sendpages() into tcp_sendpage_locked()
ip, udp: Support MSG_SPLICE_PAGES
ip, udp: Make sendmsg(MSG_SPLICE_PAGES) copy unspliceable data
udp: Convert udp_sendpage() to use MSG_SPLICE_PAGES
af_unix: Support MSG_SPLICE_PAGES
af_unix: Make sendmsg(MSG_SPLICE_PAGES) copy unspliceable data
crypto: af_alg: Pin pages rather than ref'ing if appropriate
crypto: af_alg: Use netfs_extract_iter_to_sg() to create scatterlists
crypto: af_alg: Indent the loop in af_alg_sendmsg()
crypto: af_alg: Support MSG_SPLICE_PAGES
crypto: af_alg: Convert af_alg_sendpage() to use MSG_SPLICE_PAGES
crypto: af_alg/hash: Support MSG_SPLICE_PAGES
splice, net: Use sendmsg(MSG_SPLICE_PAGES) rather than ->sendpage()
splice: Reimplement splice_to_socket() to pass multiple bufs to
sendmsg()
Remove file->f_op->sendpage
siw: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage to transmit
ceph: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage
iscsi: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage
iscsi: Assume "sendpage" is okay in iscsi_tcp_segment_map()
tcp_bpf: Make tcp_bpf_sendpage() go through
tcp_bpf_sendmsg(MSG_SPLICE_PAGES)
net: Use sendmsg(MSG_SPLICE_PAGES) not sendpage in skb_send_sock()
algif: Remove hash_sendpage*()
ceph: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage()
rds: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage
dlm: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage
sunrpc: Use sendmsg(MSG_SPLICE_PAGES) rather then sendpage
sunrpc: Rely on TCP sendmsg + MSG_SPLICE_PAGES to copy unspliceable
data
nvme: Use sendmsg(MSG_SPLICE_PAGES) rather then sendpage
kcm: Use sendmsg(MSG_SPLICE_PAGES) rather then sendpage
smc: Drop smc_sendpage() in favour of smc_sendmsg() + MSG_SPLICE_PAGES
ocfs2: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage()
drbd: Use sendmsg(MSG_SPLICE_PAGES) rather than sendmsg()
drdb: Send an entire bio in a single sendmsg
sock: Remove ->sendpage*() in favour of sendmsg(MSG_SPLICE_PAGES)

Documentation/networking/scaling.rst | 4 +-
crypto/Kconfig | 1 +
crypto/af_alg.c | 194 +++++----------
crypto/algif_aead.c | 52 ++--
crypto/algif_hash.c | 171 ++++++-------
crypto/algif_rng.c | 2 -
crypto/algif_skcipher.c | 24 +-
drivers/block/drbd/drbd_main.c | 86 +++----
drivers/infiniband/sw/siw/siw_qp_tx.c | 227 ++++-------------
drivers/net/ethernet/mediatek/mtk_wed_wo.c | 19 +-
drivers/net/ethernet/mediatek/mtk_wed_wo.h | 2 -
drivers/nvme/host/tcp.c | 63 ++---
drivers/nvme/target/tcp.c | 69 +++---
drivers/scsi/iscsi_tcp.c | 31 ++-
drivers/scsi/iscsi_tcp.h | 2 +-
drivers/scsi/libiscsi_tcp.c | 13 +-
drivers/target/iscsi/iscsi_target_util.c | 14 +-
fs/dlm/lowcomms.c | 10 +-
fs/netfs/iterator.c | 2 +-
fs/ocfs2/cluster/tcp.c | 107 ++++----
fs/splice.c | 158 +++++++++---
include/crypto/if_alg.h | 7 +-
include/linux/fs.h | 3 -
include/linux/gfp.h | 17 +-
include/linux/mm_types.h | 13 +-
include/linux/net.h | 8 -
include/linux/socket.h | 3 +
include/linux/splice.h | 2 +
include/linux/sunrpc/svc.h | 11 +-
include/linux/uio.h | 18 +-
include/net/inet_common.h | 2 -
include/net/sock.h | 6 -
include/net/tcp.h | 2 -
include/net/tls.h | 2 +-
lib/iov_iter.c | 254 ++++++++++++++++++-
mm/Makefile | 2 +-
mm/page_alloc.c | 126 ----------
mm/page_frag_alloc.c | 201 +++++++++++++++
net/appletalk/ddp.c | 1 -
net/atm/pvc.c | 1 -
net/atm/svc.c | 1 -
net/ax25/af_ax25.c | 1 -
net/caif/caif_socket.c | 2 -
net/can/bcm.c | 1 -
net/can/isotp.c | 1 -
net/can/j1939/socket.c | 1 -
net/can/raw.c | 1 -
net/ceph/messenger_v1.c | 58 ++---
net/ceph/messenger_v2.c | 89 ++-----
net/core/skbuff.c | 81 +++---
net/core/sock.c | 35 +--
net/dccp/ipv4.c | 1 -
net/dccp/ipv6.c | 1 -
net/ieee802154/socket.c | 2 -
net/ipv4/af_inet.c | 21 --
net/ipv4/ip_output.c | 104 +++++++-
net/ipv4/tcp.c | 274 ++++++---------------
net/ipv4/tcp_bpf.c | 72 +-----
net/ipv4/tcp_ipv4.c | 1 -
net/ipv4/udp.c | 54 ----
net/ipv4/udp_impl.h | 2 -
net/ipv4/udplite.c | 1 -
net/ipv6/af_inet6.c | 3 -
net/ipv6/raw.c | 1 -
net/ipv6/tcp_ipv6.c | 1 -
net/kcm/kcmsock.c | 15 +-
net/key/af_key.c | 1 -
net/l2tp/l2tp_ip.c | 1 -
net/l2tp/l2tp_ip6.c | 1 -
net/llc/af_llc.c | 1 -
net/mctp/af_mctp.c | 1 -
net/mptcp/protocol.c | 2 -
net/netlink/af_netlink.c | 1 -
net/netrom/af_netrom.c | 1 -
net/packet/af_packet.c | 2 -
net/phonet/socket.c | 2 -
net/qrtr/af_qrtr.c | 1 -
net/rds/af_rds.c | 1 -
net/rds/tcp_send.c | 86 +++----
net/rose/af_rose.c | 1 -
net/rxrpc/af_rxrpc.c | 1 -
net/sctp/protocol.c | 1 -
net/smc/af_smc.c | 29 ---
net/smc/smc_stats.c | 2 +-
net/smc/smc_stats.h | 1 -
net/smc/smc_tx.c | 16 --
net/smc/smc_tx.h | 2 -
net/socket.c | 81 +-----
net/sunrpc/svcsock.c | 83 ++-----
net/tipc/socket.c | 3 -
net/tls/tls_main.c | 25 +-
net/unix/af_unix.c | 254 ++++++++-----------
net/vmw_vsock/af_vsock.c | 3 -
net/x25/af_x25.c | 1 -
net/xdp/xsk.c | 1 -
net/xfrm/espintcp.c | 10 +-
96 files changed, 1495 insertions(+), 1874 deletions(-)
create mode 100644 mm/page_frag_alloc.c