Andreas Rohner
2014-08-31 15:47:12 UTC
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 THE_NILFS_FLUSHED flag, which is
cleared whenever new logs are written and set 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.
I am pretty sure, that there are no race conditions, but maybe someone
should check that possibility before merging this.
br,
Andreas Rohner
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 | 3 ++-
fs/nilfs2/ioctl.c | 3 ++-
fs/nilfs2/segment.c | 2 ++
fs/nilfs2/super.c | 8 ++++++++
fs/nilfs2/the_nilfs.h | 6 ++++++
5 files changed, 20 insertions(+), 2 deletions(-)
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 THE_NILFS_FLUSHED flag, which is
cleared whenever new logs are written and set 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.
I am pretty sure, that there are no race conditions, but maybe someone
should check that possibility before merging this.
br,
Andreas Rohner
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 | 3 ++-
fs/nilfs2/ioctl.c | 3 ++-
fs/nilfs2/segment.c | 2 ++
fs/nilfs2/super.c | 8 ++++++++
fs/nilfs2/the_nilfs.h | 6 ++++++
5 files changed, 20 insertions(+), 2 deletions(-)
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