Messages in this thread | | | Date | Fri, 31 Mar 2006 16:08:16 -0800 | From | "Joshua Hudson" <> | Subject | RFC replace some locking of i_sem wiht atomic_t |
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This might be a way to decrease complexity of locking in vfs.
Basic idea: for local filesystems, i_sem gets taken on several objects only to protect i_nlink. These can be removed if i_nlink is atomic.
For network filesystems, no amount of locking would ensure atomic operations anyway, so probably no loss there.
inode operations would then lock: lookup: parent create: parent link: both parents mknod: parent symlink: parent mkdir: parent unlink: parent rmdir: parent truncate: item rename: both parents
A new per-superblock semaphore vfs_link_sem would be created, to be taken first on both link and rename, dropped as soon as all other locks are taken. This prevents deadlocks in pathelogical cases. vfs_rename_sem is still needed (taken after vfs_link_sem) to prevent cycles from being created.
Grabbing the target on link doesn't do much for most filesystems because the operation is (or should be) syncronized by the page lock for each directory pages. If this change is made, it is possible to remove this locking from all the filesystems.
Note that locking of source or target is no longer necessary. Except for i_nlink, nothing can change the source or target anyway.
Comment as you will. I am competent to write this if it is wanted. I expect however that I will be flamed to ashes for this suggestion. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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