Commit Graph

12 Commits

Author SHA1 Message Date
Nikolay Borisov b5420237ec mm: refactor readahead defines in mm.h
All users of VM_MAX_READAHEAD actually convert it to kbytes and then to
pages. Define the macro explicitly as (SZ_128K / PAGE_SIZE). This
simplifies the expression in every filesystem. Also rename the macro to
VM_READAHEAD_PAGES to properly convey its meaning. Finally remove unused
VM_MIN_READAHEAD

[akpm@linux-foundation.org: fix fs/io_uring.c, per Stephen]
Link: http://lkml.kernel.org/r/20181221144053.24318-1-nborisov@suse.com
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Cc: Dominique Martinet <asmadeus@codewreck.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: David Sterba <dsterba@suse.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-03-12 10:04:01 -07:00
Jens Axboe 31b5151064 io_uring: allow workqueue item to handle multiple buffered requests
Right now we punt any buffered request that ends up triggering an
-EAGAIN to an async workqueue. This works fine in terms of providing
async execution of them, but it also can create quite a lot of work
queue items. For sequentially buffered IO, it's advantageous to
serialize the issue of them. For reads, the first one will trigger a
read-ahead, and subsequent request merely end up waiting on later pages
to complete. For writes, devices usually respond better to streamed
sequential writes.

Add state to track the last buffered request we punted to a work queue,
and if the next one is sequential to the previous, attempt to get the
previous work item to handle it. We limit the number of sequential
add-ons to the a multiple (8) of the max read-ahead size of the file.
This should be a good number for both reads and wries, as it defines the
max IO size the device can do directly.

This drastically cuts down on the number of context switches we need to
handle buffered sequential IO, and a basic test case of copying a big
file with io_uring sees a 5x speedup.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-03-06 13:00:16 -07:00
Jens Axboe 221c5eb233 io_uring: add support for IORING_OP_POLL
This is basically a direct port of bfe4037e72, which implements a
one-shot poll command through aio. Description below is based on that
commit as well. However, instead of adding a POLL command and relying
on io_cancel(2) to remove it, we mimic the epoll(2) interface of
having a command to add a poll notification, IORING_OP_POLL_ADD,
and one to remove it again, IORING_OP_POLL_REMOVE.

To poll for a file descriptor the application should submit an sqe of
type IORING_OP_POLL. It will poll the fd for the events specified in the
poll_events field.

Unlike poll or epoll without EPOLLONESHOT this interface always works in
one shot mode, that is once the sqe is completed, it will have to be
resubmitted.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Based-on-code-from: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-03-06 13:00:12 -07:00
Jens Axboe c16361c1d8 io_uring: add io_kiocb ref count
We'll use this for the POLL implementation. Regular requests will
NOT be using references, so initialize it to 0. Any real use of
the io_kiocb ref will initialize it to at least 2.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-02-28 08:24:23 -07:00
Jens Axboe 6c271ce2f1 io_uring: add submission polling
This enables an application to do IO, without ever entering the kernel.
By using the SQ ring to fill in new sqes and watching for completions
on the CQ ring, we can submit and reap IOs without doing a single system
call. The kernel side thread will poll for new submissions, and in case
of HIPRI/polled IO, it'll also poll for completions.

By default, we allow 1 second of active spinning. This can by changed
by passing in a different grace period at io_uring_register(2) time.
If the thread exceeds this idle time without having any work to do, it
will set:

sq_ring->flags |= IORING_SQ_NEED_WAKEUP.

The application will have to call io_uring_enter() to start things back
up again. If IO is kept busy, that will never be needed. Basically an
application that has this feature enabled will guard it's
io_uring_enter(2) call with:

read_barrier();
if (*sq_ring->flags & IORING_SQ_NEED_WAKEUP)
	io_uring_enter(fd, 0, 0, IORING_ENTER_SQ_WAKEUP);

instead of calling it unconditionally.

It's mandatory to use fixed files with this feature. Failure to do so
will result in the application getting an -EBADF CQ entry when
submitting IO.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-02-28 08:24:23 -07:00
Jens Axboe 6b06314c47 io_uring: add file set registration
We normally have to fget/fput for each IO we do on a file. Even with
the batching we do, the cost of the atomic inc/dec of the file usage
count adds up.

This adds IORING_REGISTER_FILES, and IORING_UNREGISTER_FILES opcodes
for the io_uring_register(2) system call. The arguments passed in must
be an array of __s32 holding file descriptors, and nr_args should hold
the number of file descriptors the application wishes to pin for the
duration of the io_uring instance (or until IORING_UNREGISTER_FILES is
called).

When used, the application must set IOSQE_FIXED_FILE in the sqe->flags
member. Then, instead of setting sqe->fd to the real fd, it sets sqe->fd
to the index in the array passed in to IORING_REGISTER_FILES.

Files are automatically unregistered when the io_uring instance is torn
down. An application need only unregister if it wishes to register a new
set of fds.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-02-28 08:24:23 -07:00
Jens Axboe edafccee56 io_uring: add support for pre-mapped user IO buffers
If we have fixed user buffers, we can map them into the kernel when we
setup the io_uring. That avoids the need to do get_user_pages() for
each and every IO.

To utilize this feature, the application must call io_uring_register()
after having setup an io_uring instance, passing in
IORING_REGISTER_BUFFERS as the opcode. The argument must be a pointer to
an iovec array, and the nr_args should contain how many iovecs the
application wishes to map.

If successful, these buffers are now mapped into the kernel, eligible
for IO. To use these fixed buffers, the application must use the
IORING_OP_READ_FIXED and IORING_OP_WRITE_FIXED opcodes, and then
set sqe->index to the desired buffer index. sqe->addr..sqe->addr+seq->len
must point to somewhere inside the indexed buffer.

The application may register buffers throughout the lifetime of the
io_uring instance. It can call io_uring_register() with
IORING_UNREGISTER_BUFFERS as the opcode to unregister the current set of
buffers, and then register a new set. The application need not
unregister buffers explicitly before shutting down the io_uring
instance.

It's perfectly valid to setup a larger buffer, and then sometimes only
use parts of it for an IO. As long as the range is within the originally
mapped region, it will work just fine.

For now, buffers must not be file backed. If file backed buffers are
passed in, the registration will fail with -1/EOPNOTSUPP. This
restriction may be relaxed in the future.

RLIMIT_MEMLOCK is used to check how much memory we can pin. A somewhat
arbitrary 1G per buffer size is also imposed.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-02-28 08:24:23 -07:00
Jens Axboe 2579f913d4 io_uring: batch io_kiocb allocation
Similarly to how we use the state->ios_left to know how many references
to get to a file, we can use it to allocate the io_kiocb's we need in
bulk.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-02-28 08:24:23 -07:00
Jens Axboe 9a56a2323d io_uring: use fget/fput_many() for file references
Add a separate io_submit_state structure, to cache some of the things
we need for IO submission.

One such example is file reference batching. io_submit_state. We get as
many references as the number of sqes we are submitting, and drop
unused ones if we end up switching files. The assumption here is that
we're usually only dealing with one fd, and if there are multiple,
hopefuly they are at least somewhat ordered. Could trivially be extended
to cover multiple fds, if needed.

On the completion side we do the same thing, except this is trivially
done just locally in io_iopoll_reap().

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-02-28 08:24:23 -07:00
Jens Axboe def596e955 io_uring: support for IO polling
Add support for a polled io_uring instance. When a read or write is
submitted to a polled io_uring, the application must poll for
completions on the CQ ring through io_uring_enter(2). Polled IO may not
generate IRQ completions, hence they need to be actively found by the
application itself.

To use polling, io_uring_setup() must be used with the
IORING_SETUP_IOPOLL flag being set. It is illegal to mix and match
polled and non-polled IO on an io_uring.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-02-28 08:24:23 -07:00
Christoph Hellwig c992fe2925 io_uring: add fsync support
Add a new fsync opcode, which either syncs a range if one is passed,
or the whole file if the offset and length fields are both cleared
to zero.  A flag is provided to use fdatasync semantics, that is only
force out metadata which is required to retrieve the file data, but
not others like metadata.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-02-28 08:24:23 -07:00
Jens Axboe 2b188cc1bb Add io_uring IO interface
The submission queue (SQ) and completion queue (CQ) rings are shared
between the application and the kernel. This eliminates the need to
copy data back and forth to submit and complete IO.

IO submissions use the io_uring_sqe data structure, and completions
are generated in the form of io_uring_cqe data structures. The SQ
ring is an index into the io_uring_sqe array, which makes it possible
to submit a batch of IOs without them being contiguous in the ring.
The CQ ring is always contiguous, as completion events are inherently
unordered, and hence any io_uring_cqe entry can point back to an
arbitrary submission.

Two new system calls are added for this:

io_uring_setup(entries, params)
	Sets up an io_uring instance for doing async IO. On success,
	returns a file descriptor that the application can mmap to
	gain access to the SQ ring, CQ ring, and io_uring_sqes.

io_uring_enter(fd, to_submit, min_complete, flags, sigset, sigsetsize)
	Initiates IO against the rings mapped to this fd, or waits for
	them to complete, or both. The behavior is controlled by the
	parameters passed in. If 'to_submit' is non-zero, then we'll
	try and submit new IO. If IORING_ENTER_GETEVENTS is set, the
	kernel will wait for 'min_complete' events, if they aren't
	already available. It's valid to set IORING_ENTER_GETEVENTS
	and 'min_complete' == 0 at the same time, this allows the
	kernel to return already completed events without waiting
	for them. This is useful only for polling, as for IRQ
	driven IO, the application can just check the CQ ring
	without entering the kernel.

With this setup, it's possible to do async IO with a single system
call. Future developments will enable polled IO with this interface,
and polled submission as well. The latter will enable an application
to do IO without doing ANY system calls at all.

For IRQ driven IO, an application only needs to enter the kernel for
completions if it wants to wait for them to occur.

Each io_uring is backed by a workqueue, to support buffered async IO
as well. We will only punt to an async context if the command would
need to wait for IO on the device side. Any data that can be accessed
directly in the page cache is done inline. This avoids the slowness
issue of usual threadpools, since cached data is accessed as quickly
as a sync interface.

Sample application: http://git.kernel.dk/cgit/fio/plain/t/io_uring.c

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-02-28 08:24:23 -07:00