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Alan Somers
a0e01997ec
metaslab_init is the slowest part of importing a mature pool, and it must be repeated hundreds of times for each top-level vdev. But its speed is dominated by a few serialized disk accesses. That can lead to import times of > 1 hour for pools with many top-level vdevs on spinny disks. Speed up the import by using a taskqueue to parallelize vdev_load across all top-level vdevs. This also requires adding mutex protection to metaslab_class_t.mc_historgram. The mc_histogram fields were unprotected when that code was first written in "Illumos 4976-4984 - metaslab improvements" (OpenZFSf3a7f6610f). The lock wasn't added until3dfb57a35e, though it's unclear exactly which fields it's supposed to protect. In any case, it wasn't until vdev_load was parallelized that any code attempted concurrent access to those fields. Sponsored by: Axcient Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Alan Somers <asomers@gmail.com> Closes #11470