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The module parameter zfs_async_block_max_blocks limits the number of blocks that can be freed by the background freeing of filesystems and snapshots (from "zfs destroy"), in one TXG. This is useful when freeing dedup blocks, becuase each zio_free() of a dedup block can require an i/o to read the relevant part of the dedup table (DDT), and will also dirty that block. zfs_async_block_max_blocks is set to 100,000 by default. For the more typical case where dedup is not used, this can have a negative performance impact on the rate of background freeing (from "zfs destroy"). For example, with recordsize=8k, and TXG's syncing once every 5 seconds, we can free only 160MB of data per second, which may be much less than the rate we can write data. This change increases zfs_async_block_max_blocks to be unlimited by default. To address the dedup freeing issue, a new tunable is introduced, zfs_max_async_dedup_frees, which limits the number of zio_free()'s of dedup blocks done by background destroys, per txg. The default is 100,000 free's (same as the old zfs_async_block_max_blocks default). Reviewed-by: Paul Dagnelie <pcd@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> Closes #10000 |
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| os | ||
| sys | ||
| .gitignore | ||
| libnvpair.h | ||
| libuutil_common.h | ||
| libuutil_impl.h | ||
| libuutil.h | ||
| libzfs_core.h | ||
| libzfs_impl.h | ||
| libzfs.h | ||
| libzutil.h | ||
| Makefile.am | ||
| thread_pool.h | ||
| zfeature_common.h | ||
| zfs_comutil.h | ||
| zfs_deleg.h | ||
| zfs_fletcher.h | ||
| zfs_namecheck.h | ||
| zfs_prop.h | ||