diff options
| -rw-r--r-- | module/zfs/mmp.c | 62 |
1 files changed, 26 insertions, 36 deletions
diff --git a/module/zfs/mmp.c b/module/zfs/mmp.c index a4771b677..c4b139757 100644 --- a/module/zfs/mmp.c +++ b/module/zfs/mmp.c @@ -198,50 +198,40 @@ mmp_thread_stop(spa_t *spa) } /* - * Randomly choose a leaf vdev, to write an MMP block to. It must be - * writable. It must not have an outstanding mmp write (if so then - * there is a problem, and a new write will also block). + * Choose a leaf vdev to write an MMP block to. It must not have an + * outstanding mmp write (if so then there is a problem, and a new write will + * also block). If there is no usable leaf in this subtree return NULL, + * otherwise return a pointer to the leaf. * - * We try 10 times to pick a random leaf without an outstanding write. - * If 90% of the leaves have pending writes, this gives us a >65% - * chance of finding one we can write to. There will be at least - * (zfs_multihost_fail_intervals) tries before the inability to write an MMP - * block causes serious problems. + * When walking the subtree, a random child is chosen as the starting point so + * that when the tree is healthy, the leaf chosen will be random with even + * distribution. If there are unhealthy vdevs in the tree, the distribution + * will be really poor only if a large proportion of the vdevs are unhealthy, + * in which case there are other more pressing problems. */ static vdev_t * -vdev_random_leaf(spa_t *spa) +mmp_random_leaf(vdev_t *vd) { - vdev_t *vd, *child; - int pending_writes = 10; + int child_idx; - ASSERT(spa); - ASSERT(spa_config_held(spa, SCL_STATE, RW_READER) == SCL_STATE); - - /* - * Since we hold SCL_STATE, neither pool nor vdev state can - * change. Therefore, if the root is not dead, there is a - * child that is not dead, and so on down to a leaf. - */ - if (!vdev_writeable(spa->spa_root_vdev)) + if (!vdev_writeable(vd)) return (NULL); - vd = spa->spa_root_vdev; - while (!vd->vdev_ops->vdev_op_leaf) { - child = vd->vdev_child[spa_get_random(vd->vdev_children)]; + if (vd->vdev_ops->vdev_op_leaf) + return (vd->vdev_mmp_pending == 0 ? vd : NULL); - if (!vdev_writeable(child)) - continue; + child_idx = spa_get_random(vd->vdev_children); + for (int offset = vd->vdev_children; offset > 0; offset--) { + vdev_t *leaf; + vdev_t *child = vd->vdev_child[(child_idx + offset) % + vd->vdev_children]; - if (child->vdev_ops->vdev_op_leaf && child->vdev_mmp_pending) { - if (pending_writes-- > 0) - continue; - else - return (NULL); - } - - vd = child; + leaf = mmp_random_leaf(child); + if (leaf) + return (leaf); } - return (vd); + + return (NULL); } static void @@ -324,8 +314,8 @@ mmp_write_uberblock(spa_t *spa) uint64_t offset; spa_config_enter(spa, SCL_STATE, FTAG, RW_READER); - vd = vdev_random_leaf(spa); - if (vd == NULL || !vdev_writeable(vd)) { + vd = mmp_random_leaf(spa->spa_root_vdev); + if (vd == NULL) { spa_config_exit(spa, SCL_STATE, FTAG); return; } |