[PATCH v4 0/1] nilfs2: add missing blkdev_issue_flush() to

[Andreas Rohner <andreas.rohner-hi6Y0CQ0nG0@public.gmane.org>]

Hi,

I have looked a bit more into the semantics of the various flags
concerning block device caching behaviour. According to
"Documentation/block/writeback_cache_control.txt" a call to
blkdev_issue_flush() is equivalent to an empty bio with the
REQ_FLUSH flag set. So there is no need to call blkdev_issue_flush()
after a call to nilfs_commit_super(). But if there is no need to write
the super block an additional call to blkdev_issue_flush() is necessary.

To avoid an overhead I introduced the nilfs->ns_flushed_device flag, 
which is set to 0  whenever new logs are written and set to 1 whenever 
the block device is flushed. If the super block was written during 
segment construction or in nilfs_sync_fs(), then blkdev_issue_flush() is 
not called.

br,
Andreas Rohner

v3->v4 (review by Ryusuke Konishi)
 * replace atomic_t with int for ns_flushed_device
 * use smp_wmb() to guarantee correct ordering

v2->v3 (review of Ryusuke Konishi)
 * Use separate atomic flag for ns_flushed_device instead of a bit flag 
   in ns_flags
 * Use smp_mb__after_atomic() after setting ns_flushed_device

v1->v2
 * Add new flag THE_NILFS_FLUSHED

Andreas Rohner (1):
  nilfs2: add missing blkdev_issue_flush() to nilfs_sync_fs()

 fs/nilfs2/file.c      | 10 +++++++++-
 fs/nilfs2/ioctl.c     | 10 +++++++++-
 fs/nilfs2/segment.c   |  4 ++++
 fs/nilfs2/super.c     | 17 +++++++++++++++++
 fs/nilfs2/the_nilfs.h |  2 ++
 5 files changed, 41 insertions(+), 2 deletions(-)

-- 
2.1.0

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