Fix L2ARC reads when compressed ARC disabled #10693
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Codecov Report
@@ Coverage Diff @@
## master #10693 +/- ##
==========================================
- Coverage 79.92% 79.75% -0.18%
==========================================
Files 394 394
Lines 124657 124661 +4
==========================================
- Hits 99636 99419 -217
- Misses 25021 25242 +221
Flags with carried forward coverage won't be shown. Click here to find out more.
Continue to review full report at Codecov.
|
12 tasks
behlendorf
approved these changes
Aug 11, 2020
When reading compressed blocks from the L2ARC, with compressed ARC disabled, arc_hdr_size() returns LSIZE rather than PSIZE, but the actual read is PSIZE. This causes l2arc_read_done() to compare the checksum against the wrong size, resulting in checksum failure. This manifests as an increase in the kstat l2_cksum_bad and the read being retried from the main pool, making the L2ARC ineffective. Add new L2ARC tests with Compressed ARC enabled/disabled Blocks are handled differently depending on the state of the zfs_compressed_arc_enabled tunable. If a block is compressed on-disk, and compressed_arc is enabled: - the block is read from disk - It is NOT decompressed - It is added to the ARC in its compressed form - l2arc_write_buffers() may write it to the L2ARC (as is) - l2arc_read_done() compares the checksum to the BP (compressed) However, if compressed_arc is disabled: - the block is read from disk - It is decompressed - It is added to the ARC (uncompressed) - l2arc_write_buffers() will use l2arc_apply_transforms() to recompress the block, before writing it to the L2ARC - l2arc_read_done() compares the checksum to the BP (compressed) - l2arc_read_done() will use l2arc_untransform() to uncompress it This test writes out a test file to a pool consisting of one disk and one cache device, then randomly reads from it. Since the arc_max in the tests is low, this will feed the L2ARC, and result in reads from the L2ARC. We compare the value of the kstat l2_cksum_bad before and after to determine if any blocks failed to survive the trip through the L2ARC. Sponsored-by: The FreeBSD Foundation Signed-off-by: Allan Jude <allanjude@freebsd.org>
allanjude
force-pushed
the
l2arc_compressed_arc_fix
branch
from
f9202ae
to
7e9d24c
Compare
17 tasks
behlendorf
reviewed
Aug 13, 2020
Signed-off-by: Allan Jude <allanjude@freebsd.org>
jsai20
pushed a commit
to jsai20/zfs
that referenced
this pull request
Mar 30, 2021
When reading compressed blocks from the L2ARC, with compressed ARC disabled, arc_hdr_size() returns LSIZE rather than PSIZE, but the actual read is PSIZE. This causes l2arc_read_done() to compare the checksum against the wrong size, resulting in checksum failure. This manifests as an increase in the kstat l2_cksum_bad and the read being retried from the main pool, making the L2ARC ineffective. Add new L2ARC tests with Compressed ARC enabled/disabled Blocks are handled differently depending on the state of the zfs_compressed_arc_enabled tunable. If a block is compressed on-disk, and compressed_arc is enabled: - the block is read from disk - It is NOT decompressed - It is added to the ARC in its compressed form - l2arc_write_buffers() may write it to the L2ARC (as is) - l2arc_read_done() compares the checksum to the BP (compressed) However, if compressed_arc is disabled: - the block is read from disk - It is decompressed - It is added to the ARC (uncompressed) - l2arc_write_buffers() will use l2arc_apply_transforms() to recompress the block, before writing it to the L2ARC - l2arc_read_done() compares the checksum to the BP (compressed) - l2arc_read_done() will use l2arc_untransform() to uncompress it This test writes out a test file to a pool consisting of one disk and one cache device, then randomly reads from it. Since the arc_max in the tests is low, this will feed the L2ARC, and result in reads from the L2ARC. We compare the value of the kstat l2_cksum_bad before and after to determine if any blocks failed to survive the trip through the L2ARC. Sponsored-by: The FreeBSD Foundation Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Allan Jude <allanjude@freebsd.org> Closes openzfs#10693
sempervictus
pushed a commit
to sempervictus/zfs
that referenced
this pull request
May 31, 2021
When reading compressed blocks from the L2ARC, with compressed ARC disabled, arc_hdr_size() returns LSIZE rather than PSIZE, but the actual read is PSIZE. This causes l2arc_read_done() to compare the checksum against the wrong size, resulting in checksum failure. This manifests as an increase in the kstat l2_cksum_bad and the read being retried from the main pool, making the L2ARC ineffective. Add new L2ARC tests with Compressed ARC enabled/disabled Blocks are handled differently depending on the state of the zfs_compressed_arc_enabled tunable. If a block is compressed on-disk, and compressed_arc is enabled: - the block is read from disk - It is NOT decompressed - It is added to the ARC in its compressed form - l2arc_write_buffers() may write it to the L2ARC (as is) - l2arc_read_done() compares the checksum to the BP (compressed) However, if compressed_arc is disabled: - the block is read from disk - It is decompressed - It is added to the ARC (uncompressed) - l2arc_write_buffers() will use l2arc_apply_transforms() to recompress the block, before writing it to the L2ARC - l2arc_read_done() compares the checksum to the BP (compressed) - l2arc_read_done() will use l2arc_untransform() to uncompress it This test writes out a test file to a pool consisting of one disk and one cache device, then randomly reads from it. Since the arc_max in the tests is low, this will feed the L2ARC, and result in reads from the L2ARC. We compare the value of the kstat l2_cksum_bad before and after to determine if any blocks failed to survive the trip through the L2ARC. Sponsored-by: The FreeBSD Foundation Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Allan Jude <allanjude@freebsd.org> Closes openzfs#10693
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Signed-off-by: Allan Jude allanjude@freebsd.org
Sponsored-by: The FreeBSD Foundation
Motivation and Context
When reading compressed blocks from the L2ARC, with compressed ARC disabled, arc_hdr_size() returns LSIZE rather than PSIZE, but the actual read is PSIZE. This causes l2arc_read_done() to compare the checksum against the wrong size, resulting in checksum failure.
This manifests as an increase in the kstat l2_cksum_bad and the read being retried from the main pool, making the L2ARC ineffective.
Description
This bug was discovered while creating the tests introduced in #10692
How Has This Been Tested?
With this change, the new test now passed.
Types of changes
Checklist:
Signed-off-by.