3b9fd93d0b
The zfs_znode_hold_enter() / zfs_znode_hold_exit() functions are used to serialize access to a znode and its SA buffer while the object is being created or destroyed. This kind of locking would normally reside in the znode itself but in this case that's impossible because the znode and SA buffer may not yet exist. Therefore the locking is handled externally with an array of mutexs and AVLs trees which contain per-object locks. In zfs_znode_hold_enter() a per-object lock is created as needed, inserted in to the correct AVL tree and finally the per-object lock is held. In zfs_znode_hold_exit() the process is reversed. The per-object lock is released, removed from the AVL tree and destroyed if there are no waiters. This scheme has two important properties: 1) No memory allocations are performed while holding one of the z_hold_locks. This ensures evict(), which can be called from direct memory reclaim, will never block waiting on a z_hold_locks which just happens to have hashed to the same index. 2) All locks used to serialize access to an object are per-object and never shared. This minimizes lock contention without creating a large number of dedicated locks. On the downside it does require znode_lock_t structures to be frequently allocated and freed. However, because these are backed by a kmem cache and very short lived this cost is minimal. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Issue #4106 |
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| avl | ||
| nvpair | ||
| unicode | ||
| zcommon | ||
| zfs | ||
| zpios | ||
| .gitignore | ||
| Makefile.in | ||