diff options
Diffstat (limited to 'fs/xfs/libxfs/xfs_defer.c')
| -rw-r--r-- | fs/xfs/libxfs/xfs_defer.c | 79 |
1 files changed, 72 insertions, 7 deletions
diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c index c221d0ecd52e..613c5cf19436 100644 --- a/fs/xfs/libxfs/xfs_defer.c +++ b/fs/xfs/libxfs/xfs_defer.c @@ -81,6 +81,10 @@ * - For each work item attached to the log intent item, * * Perform the described action. * * Attach the work item to the log done item. + * * If the result of doing the work was -EAGAIN, ->finish work + * wants a new transaction. See the "Requesting a Fresh + * Transaction while Finishing Deferred Work" section below for + * details. * * The key here is that we must log an intent item for all pending * work items every time we roll the transaction, and that we must log @@ -88,6 +92,34 @@ * we can perform complex remapping operations, chaining intent items * as needed. * + * Requesting a Fresh Transaction while Finishing Deferred Work + * + * If ->finish_item decides that it needs a fresh transaction to + * finish the work, it must ask its caller (xfs_defer_finish) for a + * continuation. The most likely cause of this circumstance are the + * refcount adjust functions deciding that they've logged enough items + * to be at risk of exceeding the transaction reservation. + * + * To get a fresh transaction, we want to log the existing log done + * item to prevent the log intent item from replaying, immediately log + * a new log intent item with the unfinished work items, roll the + * transaction, and re-call ->finish_item wherever it left off. The + * log done item and the new log intent item must be in the same + * transaction or atomicity cannot be guaranteed; defer_finish ensures + * that this happens. + * + * This requires some coordination between ->finish_item and + * defer_finish. Upon deciding to request a new transaction, + * ->finish_item should update the current work item to reflect the + * unfinished work. Next, it should reset the log done item's list + * count to the number of items finished, and return -EAGAIN. + * defer_finish sees the -EAGAIN, logs the new log intent item + * with the remaining work items, and leaves the xfs_defer_pending + * item at the head of the dop_work queue. Then it rolls the + * transaction and picks up processing where it left off. It is + * required that ->finish_item must be careful to leave enough + * transaction reservation to fit the new log intent item. + * * This is an example of remapping the extent (E, E+B) into file X at * offset A and dealing with the extent (C, C+B) already being mapped * there: @@ -104,21 +136,26 @@ * | Intent to add rmap (X, E, A, B) | * +-------------------------------------------------+ * | Reduce refcount for extent (C, B) | t2 - * | Done reducing refcount for extent (C, B) | + * | Done reducing refcount for extent (C, 9) | + * | Intent to reduce refcount for extent (C+9, B-9) | + * | (ran out of space after 9 refcount updates) | + * +-------------------------------------------------+ + * | Reduce refcount for extent (C+9, B+9) | t3 + * | Done reducing refcount for extent (C+9, B-9) | * | Increase refcount for extent (E, B) | * | Done increasing refcount for extent (E, B) | * | Intent to free extent (C, B) | * | Intent to free extent (F, 1) (refcountbt block) | * | Intent to remove rmap (F, 1, REFC) | * +-------------------------------------------------+ - * | Remove rmap (X, C, A, B) | t3 + * | Remove rmap (X, C, A, B) | t4 * | Done removing rmap (X, C, A, B) | * | Add rmap (X, E, A, B) | * | Done adding rmap (X, E, A, B) | * | Remove rmap (F, 1, REFC) | * | Done removing rmap (F, 1, REFC) | * +-------------------------------------------------+ - * | Free extent (C, B) | t4 + * | Free extent (C, B) | t5 * | Done freeing extent (C, B) | * | Free extent (D, 1) | * | Done freeing extent (D, 1) | @@ -141,6 +178,9 @@ * - Intent to free extent (C, B) * - Intent to free extent (F, 1) (refcountbt block) * - Intent to remove rmap (F, 1, REFC) + * + * Note that the continuation requested between t2 and t3 is likely to + * reoccur. */ static const struct xfs_defer_op_type *defer_op_types[XFS_DEFER_OPS_TYPE_MAX]; @@ -323,7 +363,16 @@ xfs_defer_finish( dfp->dfp_count--; error = dfp->dfp_type->finish_item(*tp, dop, li, dfp->dfp_done, &state); - if (error) { + if (error == -EAGAIN) { + /* + * Caller wants a fresh transaction; + * put the work item back on the list + * and jump out. + */ + list_add(li, &dfp->dfp_work); + dfp->dfp_count++; + break; + } else if (error) { /* * Clean up after ourselves and jump out. * xfs_defer_cancel will take care of freeing @@ -335,9 +384,25 @@ xfs_defer_finish( goto out; } } - /* Done with the dfp, free it. */ - list_del(&dfp->dfp_list); - kmem_free(dfp); + if (error == -EAGAIN) { + /* + * Caller wants a fresh transaction, so log a + * new log intent item to replace the old one + * and roll the transaction. See "Requesting + * a Fresh Transaction while Finishing + * Deferred Work" above. + */ + dfp->dfp_intent = dfp->dfp_type->create_intent(*tp, + dfp->dfp_count); + dfp->dfp_done = NULL; + list_for_each(li, &dfp->dfp_work) + dfp->dfp_type->log_item(*tp, dfp->dfp_intent, + li); + } else { + /* Done with the dfp, free it. */ + list_del(&dfp->dfp_list); + kmem_free(dfp); + } if (cleanup_fn) cleanup_fn(*tp, state, error); |