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authorBrian Behlendorf <[email protected]>2018-03-13 10:52:48 -0700
committerGitHub <[email protected]>2018-03-13 10:52:48 -0700
commitde4f8d5d2620b550b99a7bdbfbeb49214a38dc79 (patch)
tree17e9ccdbde525d237b684eef40bf910b629589e2 /lib
parenta6cc97566c54255c98612c801f2c9d9be2d0e8f8 (diff)
OpenZFS 9188 - increase size of dbuf cache to reduce indirect block decompression
With compressed ARC (bug 6950) we use up to 25% of our CPU to decompress indirect blocks, under a workload of random cached reads. To reduce this decompression cost, we would like to increase the size of the dbuf cache so that more indirect blocks can be stored uncompressed. If we are caching entire large files of recordsize=8K, the indirect blocks use 1/64th as much memory as the data blocks (assuming they have the same compression ratio). We suggest making the dbuf cache be 1/32nd of all memory, so that in this scenario we should be able to keep all the indirect blocks decompressed in the dbuf cache. (We want it to be more than the 1/64th that the indirect blocks would use because we need to cache other stuff in the dbuf cache as well.) In real world workloads, this won't help as dramatically as the example above, but we think it's still worth it because the risk of decreasing performance is low. The potential negative performance impact is that we will be slightly reducing the size of the ARC (by ~3%). Porting Notes: * Added modules options to zfs-module-parameters.5 man page. * Preserved scaling based on target ARC size rather than max ARC size. Authored by: George Wilson <[email protected]> Reviewed by: Dan Kimmel <[email protected]> Reviewed by: Prashanth Sreenivasa <[email protected]> Reviewed by: Paul Dagnelie <[email protected]> Reviewed-by: Richard Elling <[email protected]> Reviewed-by: George Melikov <[email protected]> Reviewed-by: Giuseppe Di Natale <[email protected]> Ported-by: Brian Behlendorf <[email protected]> OpenZFS-issue: https://www.illumos.org/issues/9188 OpenZFS-commit: https://github.com/openzfs/openzfs/pull/564 Upstream bug: DLPX-46942 Closes #7273
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