OpenZFS 9577 - remove zfs_dbuf_evict_key tsd #7602
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The zfs_dbuf_evict_key TSD (thread-specific data) is not necessary - we can instead pass a flag down in a few places to prevent recursive dbuf eviction. Making this change has 3 benefits: 1. The code semantics are easier to understand. 2. On Linux, performance is improved, because creating/removing TSD values (by setting to NULL vs non-NULL) is expensive, and we do it very often. 3. According to Nexenta, the current semantics can cause a deadlock when concurrently calling dmu_objset_evict_dbufs() (which is rare today, but they are working on a "parallel unmount" change that triggers this more easily): Porting Notes: * Minor conflict with OpenZFS 9337 which has not yet been ported. Authored by: Matthew Ahrens <mahrens@delphix.com> Reviewed by: George Wilson <george.wilson@delphix.com> Reviewed by: Serapheim Dimitropoulos <serapheim.dimitro@delphix.com> Approved by: Ported-by: Brian Behlendorf <behlendorf1@llnl.gov> OpenZFS-issue: https://illumos.org/issues/9577 OpenZFS-commit: openzfs/openzfs@68611d3 Upstream bug: DLPX-58547
Codecov Report
@@ Coverage Diff @@
## master #7602 +/- ##
==========================================
+ Coverage 77.43% 77.45% +0.02%
==========================================
Files 362 362
Lines 110316 110314 -2
==========================================
+ Hits 85418 85443 +25
+ Misses 24898 24871 -27
Continue to review full report at Codecov.
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behlendorf
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gmelikov
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Jun 5, 2018
ahrens
approved these changes
Jun 12, 2018
tonyhutter
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to tonyhutter/zfs
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Jan 30, 2019
The zfs_dbuf_evict_key TSD (thread-specific data) is not necessary - we can instead pass a flag down in a few places to prevent recursive dbuf eviction. Making this change has 3 benefits: 1. The code semantics are easier to understand. 2. On Linux, performance is improved, because creating/removing TSD values (by setting to NULL vs non-NULL) is expensive, and we do it very often. 3. According to Nexenta, the current semantics can cause a deadlock when concurrently calling dmu_objset_evict_dbufs() (which is rare today, but they are working on a "parallel unmount" change that triggers this more easily): Porting Notes: * Minor conflict with OpenZFS 9337 which has not yet been ported. Authored by: Matthew Ahrens <mahrens@delphix.com> Reviewed by: George Wilson <george.wilson@delphix.com> Reviewed by: Serapheim Dimitropoulos <serapheim.dimitro@delphix.com> Reviewed by: Brad Lewis <brad.lewis@delphix.com> Reviewed-by: George Melikov <mail@gmelikov.ru> Ported-by: Brian Behlendorf <behlendorf1@llnl.gov> OpenZFS-issue: https://illumos.org/issues/9577 OpenZFS-commit: openzfs/openzfs#645 External-issue: DLPX-58547 Closes openzfs#7602
tonyhutter
pushed a commit
that referenced
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Mar 4, 2019
The zfs_dbuf_evict_key TSD (thread-specific data) is not necessary - we can instead pass a flag down in a few places to prevent recursive dbuf eviction. Making this change has 3 benefits: 1. The code semantics are easier to understand. 2. On Linux, performance is improved, because creating/removing TSD values (by setting to NULL vs non-NULL) is expensive, and we do it very often. 3. According to Nexenta, the current semantics can cause a deadlock when concurrently calling dmu_objset_evict_dbufs() (which is rare today, but they are working on a "parallel unmount" change that triggers this more easily): Porting Notes: * Minor conflict with OpenZFS 9337 which has not yet been ported. Authored by: Matthew Ahrens <mahrens@delphix.com> Reviewed by: George Wilson <george.wilson@delphix.com> Reviewed by: Serapheim Dimitropoulos <serapheim.dimitro@delphix.com> Reviewed by: Brad Lewis <brad.lewis@delphix.com> Reviewed-by: George Melikov <mail@gmelikov.ru> Ported-by: Brian Behlendorf <behlendorf1@llnl.gov> OpenZFS-issue: https://illumos.org/issues/9577 OpenZFS-commit: openzfs/openzfs#645 External-issue: DLPX-58547 Closes #7602
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Description
The zfs_dbuf_evict_key TSD (thread-specific data) is not necessary -
we can instead pass a flag down in a few places to prevent recursive
dbuf eviction. Making this change has 3 benefits:
TSD values (by setting to NULL vs non-NULL) is expensive, and
we do it very often.
deadlock when concurrently calling dmu_objset_evict_dbufs()
(which is rare today, but they are working on a "parallel
unmount" change that triggers this more easily):
Porting Notes:
Motivation and Context
OpenZFS-issue: https://illumos.org/issues/9577
OpenZFS-commit: openzfs/openzfs@68611d3
Upstream bug: DLPX-58547
Possibily the root cause of #6880.
How Has This Been Tested?
Locally compiled.
Types of changes
Checklist:
Signed-off-by.