Andreas Rohner
2014-09-09 16:35:39 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 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.
On most modern architectures loads and stores of single word integers
are atomic. I still used atomic_t for ns_flushed_device for
documentation purposes. I only use atomic_read() and atomic_set(). Both
are inline functions, which compile down to simple loads and stores on
modern architectures, so there is no performance benefit in using a
simple int instead.
br,
Andreas Rohner
v2->v3 (based on 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 | 6 +++++-
fs/nilfs2/ioctl.c | 6 +++++-
fs/nilfs2/segment.c | 4 ++++
fs/nilfs2/super.c | 12 ++++++++++++
fs/nilfs2/the_nilfs.c | 1 +
fs/nilfs2/the_nilfs.h | 2 ++
6 files changed, 29 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 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.
On most modern architectures loads and stores of single word integers
are atomic. I still used atomic_t for ns_flushed_device for
documentation purposes. I only use atomic_read() and atomic_set(). Both
are inline functions, which compile down to simple loads and stores on
modern architectures, so there is no performance benefit in using a
simple int instead.
br,
Andreas Rohner
v2->v3 (based on 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 | 6 +++++-
fs/nilfs2/ioctl.c | 6 +++++-
fs/nilfs2/segment.c | 4 ++++
fs/nilfs2/super.c | 12 ++++++++++++
fs/nilfs2/the_nilfs.c | 1 +
fs/nilfs2/the_nilfs.h | 2 ++
6 files changed, 29 insertions(+), 2 deletions(-)
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