[PATCH v2 0/8] change sb_writers to use percpu_rw_semaphore

[Oleg Nesterov <oleg@redhat.com>]

Jan, please consider this series. I didn't dare to preserve your acks,
I hope you can ack v2 too.

The only essential change is that I dropped the lockdep improvements
as we discussed. This means that 8/8 was changed a bit, and I decided
to add the new documentation patch, see 3/8.

6/8 is new too, I forgot to do this in V1.

To remind, I tested this with the following script:

        dd if=/dev/zero of=TEST.img bs=1MiB count=4000
        dd if=/dev/zero of=SCRATCH.img bs=1MiB count=4000

        losetup --find --show TEST.img
        losetup --find --show SCRATCH.img

        mkfs.xfs -f /dev/loop0
        mkfs.xfs -f /dev/loop1

        mkdir -p TEST SCRATCH

        mount /dev/loop0 TEST
        mount /dev/loop1 SCRATCH

        TEST_DEV=/dev/loop0 TEST_DIR=TEST SCRATCH_DEV=/dev/loop1 SCRATCH_MNT=SCRATCH \
        ./check `grep -il freeze tests/*/???`

seems to work:

	Ran: generic/068 generic/085 generic/280 generic/311 xfs/011 xfs/119 xfs/297
        Passed all 7 tests

and I see nothing interesting in dmesg.

If I replace mkfs.xfs above with mkfs.btrfs or mkfs.ext4 everything
looks fine too:

	FSTYP         -- btrfs
	PLATFORM      -- Linux/x86_64 intel-canoepass-10 4.2.0-rc6+
	MKFS_OPTIONS  -- /dev/loop1
	MOUNT_OPTIONS -- -o context=system_u:object_r:nfs_t:s0 /dev/loop1 SCRATCH

	generic/068 60s ... 53s
	generic/085 24s ... 16s
	generic/280 2s ... [not run] disk quotas not supported by this filesystem type: btrfs
	generic/311 165s ... 136s
	xfs/011 20s ... [not run] not suitable for this filesystem type: btrfs
	xfs/119 22s ... [not run] not suitable for this filesystem type: btrfs
	xfs/297 270s ... [not run] not suitable for this filesystem type: btrfs
	Ran: generic/068 generic/085 generic/311
	Not run: generic/280 xfs/011 xfs/119 xfs/297
	Passed all 3 tests

and	

	FSTYP         -- ext4
	PLATFORM      -- Linux/x86_64 intel-canoepass-10 4.2.0-rc6+
	MKFS_OPTIONS  -- /dev/loop1
	MOUNT_OPTIONS -- -o acl,user_xattr -o context=system_u:object_r:nfs_t:s0 /dev/loop1 SCRATCH

	generic/068 53s ... 52s
	generic/085 16s ... 8s
	generic/280 2s ... 4s
	generic/311 136s ... 173s
	xfs/011 20s ... [not run] not suitable for this filesystem type: ext4
	xfs/119 22s ... [not run] not suitable for this filesystem type: ext4
	xfs/297 270s ... [not run] not suitable for this filesystem type: ext4
	Ran: generic/068 generic/085 generic/280 generic/311
	Not run: xfs/011 xfs/119 xfs/297
	Passed all 4 tests

Oleg.

 arch/Kconfig                  |    1 -
 fs/btrfs/transaction.c        |    8 +--
 fs/super.c                    |  167 ++++++++++++++++++-----------------------
 fs/xfs/xfs_aops.c             |    6 +-
 include/linux/fs.h            |   23 +++---
 include/linux/percpu-rwsem.h  |   20 +++++
 init/Kconfig                  |    1 -
 kernel/locking/Makefile       |    3 +-
 kernel/locking/percpu-rwsem.c |   13 +++
 lib/Kconfig                   |    3 -
 10 files changed, 122 insertions(+), 123 deletions(-)