fs: simplify handling of zero sized reads in __blockdev_direct_IO

Reject zero sized reads as soon as we know our I/O length, and don't
borther with locks or allocations that might have to be cleaned up
otherwise.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
fs: always maintain i_dio_count

Maintain i_dio_count for all filesystems, not just those using DIO_LOCKING.
This these filesystems to also protect truncate against direct I/O requests
by using common code.  Right now the only non-DIO_LOCKING filesystem that
appears to do so is XFS, which uses an opencoded variant of the i_dio_count
scheme.

Behaviour doesn't change for filesystems never calling inode_dio_wait.
For ext4 behaviour changes when using the dioread_nonlock option, which
previously was missing any protection between truncate and direct I/O reads.
For ocfs2 that handcrafted i_dio_count manipulations are replaced with
the common code now enable.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
 fs: move inode_dio_done to the end_io handler

For filesystems that delay their end_io processing we should keep our
i_dio_count until the the processing is done.  Enable this by moving
the inode_dio_done call to the end_io handler if one exist.  Note that
the actual move to the workqueue for ext4 and XFS is not done in
this patch yet, but left to the filesystem maintainers.  At least
for XFS it's not needed yet either as XFS has an internal equivalent
to i_dio_count.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
direct-io: separate fields only used in the submission path from struct dio

This large, but largely mechanic, patch moves all fields in struct dio
that are only used in the submission path into a separate on stack
data structure. This has the advantage that the memory is very likely
cache hot, which is not guaranteed for memory fresh out of kmalloc.

This also gives gcc more optimization potential because it can easier
determine that there are no external aliases for these variables.

The sdio initialization is a initialization now instead of memset.
This allows gcc to break sdio into individual fields and optimize
away unnecessary zeroing (after all the functions are inlined)

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
direct-io: fix a wrong comment

There's nothing on the stack, even before my changes.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
direct-io: rearrange fields in dio/dio_submit to avoid holes

Fix most problems reported by pahole.

There is still a weird 104 byte hole after map_bh. I'm not sure what
causes this.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
direct-io: use a slab cache for struct dio

A direct slab call is slightly faster than kmalloc and can be better cached
per CPU. It also avoids rounding to the next kmalloc slab.

In addition this enforces cache line alignment for struct dio to avoid
any false sharing.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
direct-io: separate map_bh from dio

Only a single b_private field in the map_bh buffer head is needed after
the submission path. Move map_bh separately to avoid storing
this information in the long term slab.

This avoids the weird 104 byte hole in struct dio_submit which also needed
to be memseted early.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
direct-io: inline the complete submission path

Add inlines to all the submission path functions. While this increases
code size it also gives gcc a lot of optimization opportunities
in this critical hotpath.

In particular -- together with some other changes -- this
allows gcc to get rid of the unnecessary clearing of
sdio at the beginning and optimize the messy parameter passing.
Any non inlining of a function which takes a sdio parameter
would break this optimization because they cannot be done if the
address of a structure is taken.

Note that benefits are only seen with CONFIG_OPTIMIZE_INLINING
and CONFIG_CC_OPTIMIZE_FOR_SIZE both set to off.

This gives about 2.2% improvement on a large database benchmark
with a high IOPS rate.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
direct-io: merge direct_io_walker into __blockdev_direct_IO

This doesn't change anything for the compiler, but hch thought it would
make the code clearer.

I moved the reference counting into its own little inline.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
fs/direct-io.c: calculate fs_count correctly in get_more_blocks()

In get_more_blocks(), we use dio_count to calcuate fs_count and do some
tricky things to increase fs_count if dio_count isn't aligned.  But
actually it still has some corner cases that can't be coverd.  See the
following example:

	dio_write foo -s 1024 -w 4096

(direct write 4096 bytes at offset 1024).  The same goes if the offset
isn't aligned to fs_blocksize.

In this case, the old calculation counts fs_count to be 1, but actually we
will write into 2 different blocks (if fs_blocksize=4096).  The old code
just works, since it will call get_block twice (and may have to allocate
and create extents twice for filesystems like ext4).  So we'd better call
get_block just once with the proper fs_count.

Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
dio: optimize cache misses in the submission path

Some investigation of a transaction processing workload showed that a
major consumer of cycles in __blockdev_direct_IO is the cache miss while
accessing the block size.  This is because it has to walk the chain from
block_dev to gendisk to queue.

The block size is needed early on to check alignment and sizes.  It's only
done if the check for the inode block size fails.  But the costly block
device state is unconditionally fetched.

- Reorganize the code to only fetch block dev state when actually
  needed.

Then do a prefetch on the block dev early on in the direct IO path.  This
is worth it, because there is substantial code run before we actually
touch the block dev now.

- I also added some unlikelies to make it clear the compiler that block
  device fetch code is not normally executed.

This gave a small, but measurable improvement on a large database
benchmark (about 0.3%)

[akpm@linux-foundation.org: coding-style fixes]
[sfr@canb.auug.org.au: using prefetch requires including prefetch.h]
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: 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>
fs/direct-io.c: adjust suspicious bit operation

READ is 0, so the result of the bit-and operation is 0.  Rewrite with == as
done elsewhere in the same file.

This problem was found using Coccinelle (http://coccinelle.lip6.fr/).

Signed-off-by: Julia Lawall <julia@diku.dk>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
block: move down direct IO plugging

Move unplugging for direct I/O from around ->direct_IO() down to
do_blockdev_direct_IO(). This implicitly adds plugging for direct
writes.

CC: Li Shaohua <shli@fusionio.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
direct-io: don't read inode->i_blkbits multiple times

Since directio can work on a raw block device, and the block size of the
device can change under it, we need to do the same thing that
fs/buffer.c now does: read the block size a single time, using
ACCESS_ONCE().

Reading it multiple times can get different results, which will then
confuse the code because it actually encodes the i_blksize in
relationship to the underlying logical blocksize.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
fs: Fix possible use-after-free with AIO

Running AIO is pinning inode in memory using file reference. Once AIO
is completed using aio_complete(), file reference is put and inode can
be freed from memory. So we have to be sure that calling aio_complete()
is the last thing we do with the inode.

CC: Christoph Hellwig <hch@infradead.org>
CC: Jens Axboe <axboe@kernel.dk>
CC: Jeff Moyer <jmoyer@redhat.com>
CC: stable@vger.kernel.org
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
direct-io: fix boundary block handling

When we read/write a file sequentially, we will read/write not only the
data blocks but also the indirect blocks that may not be physically
adjacent to the data blocks.  So filesystems set the BH_Boundary flag to
submit the previous I/O before reading/writing an indirect block.

However the generic direct IO code mishandles buffer_boundary(), setting
sdio->boundary before each submit_page_section() call which results in
sending only one page bios as underlying code thinks this page is the last
in the contiguous extent.  So fix the problem by setting sdio->boundary
only if the current page is really the last one in the mapped extent.

With this patch and "direct-io: submit bio after boundary buffer is added
to it" I've measured about 10% throughput improvement of direct IO reads
on ext3 with SATA harddrive (from 90 MB/s to 100 MB/s).  With ramdisk, the
improvement was about 3-fold (from 350 MB/s to 1.2 GB/s).  For other
filesystems (such as ext4), the improvements won't be as visible because
the frequency of BH_Boundary flag being set is much smaller.

Signed-off-by: Jan Kara <jack@suse.cz>
Reported-by: Kazuya Mio <k-mio@sx.jp.nec.com>
Tested-by: Kazuya Mio <k-mio@sx.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
direct-io: submit bio after boundary buffer is added to it

Currently, dio_send_cur_page() submits bio before current page and cached
sdio->cur_page is added to the bio if sdio->boundary is set.  This is
actually wrong because sdio->boundary means the current buffer is the last
one before metadata needs to be read.  So we should rather submit the bio
after the current page is added to it.

Signed-off-by: Jan Kara <jack@suse.cz>
Reported-by: Kazuya Mio <k-mio@sx.jp.nec.com>
Tested-by: Kazuya Mio <k-mio@sx.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>