This bug was fixed in the package zfs-linux - 0.7.5-1ubuntu6
---------------
zfs-linux (0.7.5-1ubuntu6) bionic; urgency=medium
* Fix ARC hit rate (LP: #1755158)
- Upstream fix, commit 0873bb6337452e3e028e40f5dad945b30deab185,
fixes issue that can impact ARC hit rate especially with a
small ARC
-- Colin Ian King <colin.k...@canonical.com> Mon, 12 Mar 2018 12:40:22
+0000
** Changed in: zfs-linux (Ubuntu Bionic)
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1755158
Title:
Fix ARC hit rate
Status in linux package in Ubuntu:
Fix Committed
Status in zfs-linux package in Ubuntu:
Fix Released
Status in linux source package in Bionic:
Fix Committed
Status in zfs-linux source package in Bionic:
Fix Released
Bug description:
Upstream commit:
https://github.com/zfsonlinux/zfs/pull/6989/commits/e0014d56c3c21d53a71c436d54e10a456acb190d
"When the compressed ARC feature was added in commit d3c2ae1
the method of reference counting in the ARC was modified. As
part of this accounting change the arc_buf_add_ref() function
was removed entirely.
This would have be fine but the arc_buf_add_ref() function
served a second undocumented purpose of updating the ARC access
information when taking a hold on a dbuf. Without this logic
in place a cached dbuf would not migrate its associated
arc_buf_hdr_t to the MFU list. This would negatively impact
the ARC hit rate, particularly on systems with a small ARC."
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