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Refactor dmu_prefetch(). #15076

Merged
merged 1 commit into from
Aug 7, 2023
Merged

Refactor dmu_prefetch(). #15076

merged 1 commit into from
Aug 7, 2023

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@amotin amotin commented Jul 17, 2023 •
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  • Split dmu_prefetch_dnode() from dmu_prefetch() into a separate function. It is quite inconvenient to read the code where len = 0 means dnode prefetch instead indirect/data prefetch. One function doing both has no benefits, since the code paths are independent.
  • Improve dmu_prefetch() handling of long block ranges. Instead of limiting L0 data length to prefetch for to dmu_prefetch_max, make dmu_prefetch_max limit the actual amount of prefetch at the specified level, and, if there is more, prefetch all the rest at higher indirection level. It should improve random access times within the prefetched range of any length, reducing importance of specific dmu_prefetch_max value.

How Has This Been Tested?

  • Manually called dmu_prefetch() for 256MB L0 range. Observed with DTrace 32768 4KB L0 dbuf_prefetch() calls for the first 128MB (dmu_prefetch_max), followed by 127 32KB L1 dbuf_prefetch() calls for the rest.
  • Manually called dmu_prefetch() for 16GB L0 range. Observed with DTrace 32768 4KB L0 dbuf_prefetch() calls for the first 128MB (dmu_prefetch_max), followed by 63 32KB L2 dbuf_prefetch() calls for the rest.

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Performance enhancement (non-breaking change which improves efficiency)
  • Code cleanup (non-breaking change which makes code smaller or more readable)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
  • Documentation (a change to man pages or other documentation)

Checklist:

@amotin
Refactor dmu_prefetch().
b6f09da 
 - Split dmu_prefetch_dnode() from dmu_prefetch() into a separate
function.  It is quite inconvenient to read the code where len = 0
means dnode prefetch instead indirect/data prefetch.  One function
doing both has no benefits, since the code paths are independent.
 - Improve dmu_prefetch() handling of long block ranges.  Instead
of limiting L0 data length to prefetch for to dmu_prefetch_max,
make dmu_prefetch_max limit the actual amount of prefetch at the
specified level, and, if there is more, prefetch all the rest at
higher indirection level.  It should improve random access times
within the prefetched range of any length, reducing importance of
specific dmu_prefetch_max value.

Signed-off-by:	Alexander Motin <[email protected]>
Sponsored by:	iXsystems, Inc.
@amotin amotin added Status: Code Review Needed Ready for review and testing Type: Performance Performance improvement or performance problem labels Jul 17, 2023
@amotin amotin requested review from ahrens and pcd1193182 July 17, 2023 21:29
@behlendorf behlendorf added Status: Accepted Ready to integrate (reviewed, tested) and removed Status: Code Review Needed Ready for review and testing labels Aug 1, 2023
@behlendorf behlendorf merged commit 6c94e64 into openzfs:master Aug 7, 2023
@amotin amotin deleted the dmu_prefetch branch August 8, 2023 01:39
lundman pushed a commit to openzfsonwindows/openzfs that referenced this pull request Dec 12, 2023
@amotin @lundman
Refactor dmu_prefetch().
509739b 
- Split dmu_prefetch_dnode() from dmu_prefetch() into a separate
function.  It is quite inconvenient to read the code where len = 0
means dnode prefetch instead indirect/data prefetch.  One function
doing both has no benefits, since the code paths are independent.
 - Improve dmu_prefetch() handling of long block ranges.  Instead
of limiting L0 data length to prefetch for to dmu_prefetch_max,
make dmu_prefetch_max limit the actual amount of prefetch at the
specified level, and, if there is more, prefetch all the rest at
higher indirection level.  It should improve random access times
within the prefetched range of any length, reducing importance of
specific dmu_prefetch_max value.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by:	Alexander Motin <[email protected]>
Sponsored by:	iXsystems, Inc.
Closes openzfs#15076
@amotin amotin mentioned this pull request Mar 3, 2024
Merged
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amotin added a commit to amotin/zfs that referenced this pull request Apr 17, 2024
@amotin
Refactor dmu_prefetch().
84d6363 
- Split dmu_prefetch_dnode() from dmu_prefetch() into a separate
function.  It is quite inconvenient to read the code where len = 0
means dnode prefetch instead indirect/data prefetch.  One function
doing both has no benefits, since the code paths are independent.
 - Improve dmu_prefetch() handling of long block ranges.  Instead
of limiting L0 data length to prefetch for to dmu_prefetch_max,
make dmu_prefetch_max limit the actual amount of prefetch at the
specified level, and, if there is more, prefetch all the rest at
higher indirection level.  It should improve random access times
within the prefetched range of any length, reducing importance of
specific dmu_prefetch_max value.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by:	Alexander Motin <[email protected]>
Sponsored by:	iXsystems, Inc.
Closes openzfs#15076
behlendorf pushed a commit that referenced this pull request Apr 19, 2024
@amotin @behlendorf
Refactor dmu_prefetch().
fdd97e0 
- Split dmu_prefetch_dnode() from dmu_prefetch() into a separate
function.  It is quite inconvenient to read the code where len = 0
means dnode prefetch instead indirect/data prefetch.  One function
doing both has no benefits, since the code paths are independent.
 - Improve dmu_prefetch() handling of long block ranges.  Instead
of limiting L0 data length to prefetch for to dmu_prefetch_max,
make dmu_prefetch_max limit the actual amount of prefetch at the
specified level, and, if there is more, prefetch all the rest at
higher indirection level.  It should improve random access times
within the prefetched range of any length, reducing importance of
specific dmu_prefetch_max value.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by:	Alexander Motin <[email protected]>
Sponsored by:	iXsystems, Inc.
Closes #15076
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@behlendorf behlendorf behlendorf approved these changes

@ahrens ahrens Awaiting requested review from ahrens

@pcd1193182 pcd1193182 Awaiting requested review from pcd1193182

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