fs/block-dev.c:fix performance regression in O_DIRECT writes to md block devices

For regular file, write operaion used blk_plug function.But for block
file,write operation did not use blk_plug.
This patch is also for write-cache mode for block-device.

Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
ext4: optimize test_root()

The test_root() function could potentially loop forever due to
overflow issues.  So rewrite test_root() to avoid this issue; as a
bonus, it is 38% faster when benchmarked via a test loop:

int main(int argc, char **argv)
{
	int  i;

	for (i = 0; i < 1 << 24; i++) {
		if (test_root(i, 7))
			printf("%d\n", i);
	}
}

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Linux 3.4.12

Conflicts:
	drivers/usb/host/xhci.h
Linux 3.4.13
Linux 3.4.14
Linux 3.4.15
Linux 3.4.16
Linux 3.4.17
Linux 3.4.18
Linux 3.4.19

Conflicts:
	drivers/mmc/host/sdhci.c
Linux 3.4.20
Linux 3.4.21

Conflicts:
	drivers/nfc/pn533.c
Linux 3.4.22
Linux 3.4.23
Linux 3.4.24
Linux 3.4.25
Revert "jbd2: optimize jbd2_journal_force_commit"

This reverts commit b0cc4d3ff86f553de02f3397439da2e5e192a8a8.
Revert "Revert "jbd2: optimize jbd2_journal_force_commit""

This reverts commit c01c529c84c4c958d24273406e2e03845b6372ab.
Linux 3.4.26

Conflicts:
	drivers/gpu/drm/radeon/radeon_mode.h
	fs/jbd2/transaction.c
Linux 3.4.27