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(-) -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-nilfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
