Avoid more abd_t allocations in RAIDZ/dRAID

[amotin]

RAIDZ/dRAID allocate rc_abdstruct for every column, but used it only for data columns, while parity columns allocated additional abd_t's on top of that. This change introduces abd_alloc_linear_struct(), abd_alloc_gang_struct() and abd_get_zeros_struct() to the ABD API, mirroring the existing abd_get_offset_struct() pattern, and uses them to use rc_abdstruct in remaining column cases.

How Has This Been Tested?

Profiles of RAIDZ2 write tests show a percent of ZIO pipeline CPU saved.

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)
• Quality assurance (non-breaking change which makes the code more robust against bugs)
• 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:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[robn]

Yeah, good improvement, nice one.

[behlendorf]

Nice.

[behlendorf]

I've rebased this PR on master to get another CI run with this change and #18695 both applied. There shouldn't be any issue, but no harm in making sure.