More adaptive ARC eviction. #14359
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More adaptive ARC eviction. #14359
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(sorry for the low-fidelity pic :) ) - I get a panic during import when I test this PR - looks like some incompatibility with L2ARC rebuild - |
@adamdmoss Thank you for the report. Appears I unexpectedly changed persistent L2ARC on-disk format. Added simple shim to fix it. |
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Verified fixed - thanks! |
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@amotin , thanks for making this. i currently try to test this. i have a question manpage is telling: what does a value of "500" exactly mean ? what should is set to maximise arc being used for metadata and avoid metadata eviction? proportional relation to what? |
@devZer0 It means data ghost hits cause 5 times smaller metadata cache reduction than metadata ghost hit cause data cache reduction. There is no upper limit. The higher you set it, the smaller pressure will be on metadata. It is not absolute, some metadata will likely be evicted, otherwise there will be no ghost state to indicate pressure, but after some time it should settle at some balance point where data and metadata ghost hits (read "almost cache hit but no") balance each other according to this coefficient. That is the whole point of being adaptive. |
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While there I decided to remove unusable spa argument from arc_evict_impl() and reorder remaining more logically. |
behlendorf
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Status: Accepted
Traditionally ARC adaptation was limited to MRU/MFU distribution. But for years people with metadata-centric workload demanded mechanisms to also manage data/metadata distribution, that in original ZFS was just a FIFO. As result ZFS effectively got separate states for data and metadata, minimum and maximum metadata limits etc, but it all required manual tuning, was not adaptive and in its heart remained a bad FIFO. This change removes most of existing eviction logic, rewriting it from scratch. This makes MRU/MFU adaptation individual for data and meta- data, same as the distribution between data and metadata themselves. Since most of required states separation was already done, it only required to make arcs_size state field specific per data/metadata. The adaptation logic is still based on previous concept of ghost hits, just now it balances ARC capacity between 4 states: MRU data, MRU metadata, MFU data and MFU metadata. To simplify arc_c changes instead of arc_p measured in bytes, this code uses 3 variable arc_meta, arc_pd and arc_pm, representing ARC balance between metadata and data, MRU and MFU for data, and MRU and MFU for metadata respectively as 32-bit fixed point fractions. Since we care about the math result only when need to evict, this moves all the logic from arc_adapt() to arc_evict(), that reduces per-block overhead, since per-block operations are limited to stats collection, now moved from arc_adapt() to arc_access() and using cheaper wmsums. This also allows to remove ugly ARC_HDR_DO_ADAPT flag from many places. This change also removes number of metadata specific tunables, part of which were actually not functioning correctly, since not all metadata are equal and some (like L2ARC headers) are not really evictable. Instead it introduced single opaque knob zfs_arc_meta_balance, tuning ARC's reaction on ghost hits, allowing administrator give more or less preference to metadata without setting strict limits. Some of old code parts like arc_evict_meta() are just removed, because since introduction of ABD ARC they really make no sense: only headers referenced by small number of buffers are not evictable, and they are really not evictable no matter what this code do. Instead just call arc_prune_async() if too much metadata appear not evictable. Signed-off-by: Alexander Motin <[email protected]> Sponsored by: iXsystems, Inc.
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I've noticed there is no more reason for arcstat_dnode_size to be an aggsum, since now it is read only once per arc_evict(), so I demoted it to cheaper wmsum. |
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Merged. These changes worked as intended in my testing. |
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mcmilk
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Mar 13, 2023
Traditionally ARC adaptation was limited to MRU/MFU distribution. But for years people with metadata-centric workload demanded mechanisms to also manage data/metadata distribution, that in original ZFS was just a FIFO. As result ZFS effectively got separate states for data and metadata, minimum and maximum metadata limits etc, but it all required manual tuning, was not adaptive and in its heart remained a bad FIFO. This change removes most of existing eviction logic, rewriting it from scratch. This makes MRU/MFU adaptation individual for data and meta- data, same as the distribution between data and metadata themselves. Since most of required states separation was already done, it only required to make arcs_size state field specific per data/metadata. The adaptation logic is still based on previous concept of ghost hits, just now it balances ARC capacity between 4 states: MRU data, MRU metadata, MFU data and MFU metadata. To simplify arc_c changes instead of arc_p measured in bytes, this code uses 3 variable arc_meta, arc_pd and arc_pm, representing ARC balance between metadata and data, MRU and MFU for data, and MRU and MFU for metadata respectively as 32-bit fixed point fractions. Since we care about the math result only when need to evict, this moves all the logic from arc_adapt() to arc_evict(), that reduces per-block overhead, since per-block operations are limited to stats collection, now moved from arc_adapt() to arc_access() and using cheaper wmsums. This also allows to remove ugly ARC_HDR_DO_ADAPT flag from many places. This change also removes number of metadata specific tunables, part of which were actually not functioning correctly, since not all metadata are equal and some (like L2ARC headers) are not really evictable. Instead it introduced single opaque knob zfs_arc_meta_balance, tuning ARC's reaction on ghost hits, allowing administrator give more or less preference to metadata without setting strict limits. Some of old code parts like arc_evict_meta() are just removed, because since introduction of ABD ARC they really make no sense: only headers referenced by small number of buffers are not evictable, and they are really not evictable no matter what this code do. Instead just call arc_prune_async() if too much metadata appear not evictable. Reviewed-by: Brian Behlendorf <[email protected]> Reviewed-by: Allan Jude <[email protected]> Signed-off-by: Alexander Motin <[email protected]> Sponsored by: iXsystems, Inc. Closes openzfs#14359
lundman
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Traditionally ARC adaptation was limited to MRU/MFU distribution. But for years people with metadata-centric workload demanded mechanisms to also manage data/metadata distribution, that in original ZFS was just a FIFO. As result ZFS effectively got separate states for data and metadata, minimum and maximum metadata limits etc, but it all required manual tuning, was not adaptive and in its heart remained a bad FIFO. This change removes most of existing eviction logic, rewriting it from scratch. This makes MRU/MFU adaptation individual for data and meta- data, same as the distribution between data and metadata themselves. Since most of required states separation was already done, it only required to make arcs_size state field specific per data/metadata. The adaptation logic is still based on previous concept of ghost hits, just now it balances ARC capacity between 4 states: MRU data, MRU metadata, MFU data and MFU metadata. To simplify arc_c changes instead of arc_p measured in bytes, this code uses 3 variable arc_meta, arc_pd and arc_pm, representing ARC balance between metadata and data, MRU and MFU for data, and MRU and MFU for metadata respectively as 32-bit fixed point fractions. Since we care about the math result only when need to evict, this moves all the logic from arc_adapt() to arc_evict(), that reduces per-block overhead, since per-block operations are limited to stats collection, now moved from arc_adapt() to arc_access() and using cheaper wmsums. This also allows to remove ugly ARC_HDR_DO_ADAPT flag from many places. This change also removes number of metadata specific tunables, part of which were actually not functioning correctly, since not all metadata are equal and some (like L2ARC headers) are not really evictable. Instead it introduced single opaque knob zfs_arc_meta_balance, tuning ARC's reaction on ghost hits, allowing administrator give more or less preference to metadata without setting strict limits. Some of old code parts like arc_evict_meta() are just removed, because since introduction of ABD ARC they really make no sense: only headers referenced by small number of buffers are not evictable, and they are really not evictable no matter what this code do. Instead just call arc_prune_async() if too much metadata appear not evictable. Reviewed-by: Brian Behlendorf <[email protected]> Reviewed-by: Allan Jude <[email protected]> Signed-off-by: Alexander Motin <[email protected]> Sponsored by: iXsystems, Inc. Closes openzfs#14359
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Are these changes expected to be ported to 2.1.10? |
No. Same as few other ARC refactoring PRs of mine it will stay in 2.2. Those are quite a big and invasive change for a minor release. |
pcd1193182
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Sep 26, 2023
Traditionally ARC adaptation was limited to MRU/MFU distribution. But for years people with metadata-centric workload demanded mechanisms to also manage data/metadata distribution, that in original ZFS was just a FIFO. As result ZFS effectively got separate states for data and metadata, minimum and maximum metadata limits etc, but it all required manual tuning, was not adaptive and in its heart remained a bad FIFO. This change removes most of existing eviction logic, rewriting it from scratch. This makes MRU/MFU adaptation individual for data and meta- data, same as the distribution between data and metadata themselves. Since most of required states separation was already done, it only required to make arcs_size state field specific per data/metadata. The adaptation logic is still based on previous concept of ghost hits, just now it balances ARC capacity between 4 states: MRU data, MRU metadata, MFU data and MFU metadata. To simplify arc_c changes instead of arc_p measured in bytes, this code uses 3 variable arc_meta, arc_pd and arc_pm, representing ARC balance between metadata and data, MRU and MFU for data, and MRU and MFU for metadata respectively as 32-bit fixed point fractions. Since we care about the math result only when need to evict, this moves all the logic from arc_adapt() to arc_evict(), that reduces per-block overhead, since per-block operations are limited to stats collection, now moved from arc_adapt() to arc_access() and using cheaper wmsums. This also allows to remove ugly ARC_HDR_DO_ADAPT flag from many places. This change also removes number of metadata specific tunables, part of which were actually not functioning correctly, since not all metadata are equal and some (like L2ARC headers) are not really evictable. Instead it introduced single opaque knob zfs_arc_meta_balance, tuning ARC's reaction on ghost hits, allowing administrator give more or less preference to metadata without setting strict limits. Some of old code parts like arc_evict_meta() are just removed, because since introduction of ABD ARC they really make no sense: only headers referenced by small number of buffers are not evictable, and they are really not evictable no matter what this code do. Instead just call arc_prune_async() if too much metadata appear not evictable. Reviewed-by: Brian Behlendorf <[email protected]> Reviewed-by: Allan Jude <[email protected]> Signed-off-by: Alexander Motin <[email protected]> Sponsored by: iXsystems, Inc. Closes openzfs#14359
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Oct 13, 2023
New Features - Block cloning (#13392) - Linux container support (#14070, #14097, #12263) - Scrub error log (#12812, #12355) - BLAKE3 checksums (#12918) - Corrective "zfs receive" - Vdev and zpool user properties Performance - Fully adaptive ARC (#14359) - SHA2 checksums (#13741) - Edon-R checksums (#13618) - Zstd early abort (#13244) - Prefetch improvements (#14603, #14516, #14402, #14243, #13452) - General optimization (#14121, #14123, #14039, #13680, #13613, #13606, #13576, #13553, #12789, #14925, #14948) Signed-off-by: Brian Behlendorf <[email protected]>
lundman
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Dec 12, 2023
New features: - Fully adaptive ARC eviction (openzfs#14359) - Block cloning (openzfs#13392) - Scrub error log (openzfs#12812, openzfs#12355) - Linux container support (openzfs#14070, openzfs#14097, openzfs#12263) - BLAKE3 Checksums (openzfs#12918) - Corrective "zfs receive" (openzfs#9372) Signed-off-by: Brian Behlendorf <[email protected]>
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Traditionally ARC adaptation was limited to MRU/MFU distribution. But for years people with metadata-centric workload demanded mechanisms to also manage data/metadata distribution, that in original ZFS was just a FIFO. As result ZFS effectively got separate states for data and metadata, minimum and maximum metadata limits etc, but it all required manual tuning, was not adaptive and in its heart remained a bad FIFO.
This change removes most of existing eviction logic, rewriting it from scratch. This makes MRU/MFU adaptation individual for data and metadata, same as the distribution between data and metadata themselves. Since most of required states separation was already done, it only required to make arcs_size state field specific per data/metadata.
The adaptation logic is still based on previous concept of ghost hits, just now it balances ARC capacity between 4 states: MRU data, MRU metadata, MFU data and MFU metadata. To simplify arc_c changes instead of arc_p measured in bytes, this code uses 3 variable arc_meta, arc_pd and arc_pm, representing ARC balance between metadata and data, MRU and MFU for data, and MRU and MFU for metadata respectively as 32-bit fixed point fractions. Since we care about the math result only when need to evict, this moves all the logic from arc_adapt() to arc_evict(), that reduces per-block overhead, since per-block operations are limited to stats collection, now moved from arc_adapt() to arc_access() and using cheaper wmsums. This also allows to remove ugly ARC_HDR_DO_ADAPT flag from many places.
This change also removes number of metadata specific tunables, part of which were actually not functioning correctly, since not all metadata are equal and some (like L2ARC headers) are not really evictable. Instead it introduced single opaque knob zfs_arc_meta_balance, tuning ARC's reaction on ghost hits, allowing administrator give more or less preference to metadata without setting strict limits.
Some of old code parts like arc_evict_meta() are just removed, because since introduction of ABD ARC they really make no sense: only headers referenced by small number of buffers are not evictable, and they are really not evictable no matter what this code do. Instead just call arc_prune_async() if too much metadata appear not evictable.
How Has This Been Tested?
Manually simulating different access pattern I was able to observe expected arc_meta, arc_pd and arc_pm changes.
Types of changes
Checklist:
Signed-off-by.