ARC Size

[revengineer]

In the GUI, I am setting loader tunable vfs.zfs.arc_max to 30G. However, it seems that the arc size shown in the dashboard does not exceed 10G. I am showing the output of arc_summary below. (Sorry, I cannot figure out how to make this collapsible; it's not in the tool list.) Am I missing something? Help appreciated.

Code:

root@max[~]# arc_summary

------------------------------------------------------------------------
ZFS Subsystem Report                            Sun Jul 18 20:28:34 2021
FreeBSD 12.2-RELEASE-p6                                    zpl version 5
Machine: max.korthresearch.local (amd64)                spa version 5000

ARC status:                                                      HEALTHY
        Memory throttle count:                                         0

ARC size (current):                                   100.1 %   10.0 GiB
        Target size (adaptive):                       100.0 %   10.0 GiB
        Min size (hard limit):                         27.5 %    2.7 GiB
        Max size (high water):                            3:1   10.0 GiB
        Most Frequently Used (MFU) cache size:         23.5 %    2.1 GiB
        Most Recently Used (MRU) cache size:           76.5 %    6.7 GiB
        Metadata cache size (hard limit):              75.0 %    7.5 GiB
        Metadata cache size (current):                 32.8 %    2.5 GiB
        Dnode cache size (hard limit):                 10.0 %  768.0 MiB
        Dnode cache size (current):                    80.3 %  616.4 MiB

ARC hash breakdown:
        Elements max:                                               1.2M
        Elements current:                              78.8 %     911.1k
        Collisions:                                                 1.3M
        Chain max:                                                     4
        Chains:                                                    23.9k

ARC misc:
        Deleted:                                                   16.1M
        Mutex misses:                                                308
        Eviction skips:                                           277.3k

ARC total accesses (hits + misses):                               296.4M
        Cache hit ratio:                               98.0 %     290.6M
        Cache miss ratio:                               2.0 %       5.8M
        Actual hit ratio (MFU + MRU hits):             98.0 %     290.4M
        Data demand efficiency:                        78.0 %      15.5M
        Data prefetch efficiency:                       7.8 %       2.2M

Cache hits by cache type:
        Most frequently used (MFU):                    95.0 %     276.1M
        Most recently used (MRU):                       4.9 %      14.3M
        Most frequently used (MFU) ghost:               0.1 %     386.2k
        Most recently used (MRU) ghost:                 0.1 %     206.7k

Cache hits by data type:
        Demand data:                                    4.2 %      12.1M
        Demand prefetch data:                           0.1 %     174.5k
        Demand metadata:                               95.7 %     278.2M
        Demand prefetch metadata:                     < 0.1 %      97.7k

Cache misses by data type:
        Demand data:                                   58.5 %       3.4M
        Demand prefetch data:                          35.5 %       2.1M
        Demand metadata:                                4.1 %     237.5k
        Demand prefetch metadata:                       1.9 %     113.6k

DMU prefetch efficiency:                                            7.2M
        Hit ratio:                                     24.8 %       1.8M
        Miss ratio:                                    75.2 %       5.4M

L2ARC not detected, skipping section

Tunables:
        abd_chunk_size                                              4096
        abd_scatter_enabled                                            1
        allow_redacted_dataset_mount                                   0
        anon_data_esize                                                0
        anon_metadata_esize                                            0
        anon_size                                               16506880
        arc.average_blocksize                                       8192
        arc.dnode_limit                                                0
        arc.dnode_limit_percent                                       10
        arc.dnode_reduce_percent                                      10
        arc.evict_batch_limit                                         10
        arc.eviction_pct                                             200
        arc.grow_retry                                                 0
        arc.lotsfree_percent                                          10
        arc.max                                                        0
        arc.meta_adjust_restarts                                    4096
        arc.meta_limit                                                 0
        arc.meta_limit_percent                                        75
        arc.meta_min                                                   0
        arc.meta_prune                                             10000
        arc.meta_strategy                                              1
        arc.min                                                        0
        arc.min_prefetch_ms                                            0
        arc.min_prescient_prefetch_ms                                  0
        arc.p_dampener_disable                                         1
        arc.p_min_shift                                                0
        arc.pc_percent                                                 0
        arc.shrink_shift                                               0
        arc.sys_free                                                   0
        arc_free_target                                           478573
        arc_max                                                        0
        arc_min                                                        0
        arc_no_grow_shift                                              5
        async_block_max_blocks                      18446744073709551615
        autoimport_disable                                             1
        ccw_retry_interval                                           300
        checksum_events_per_second                                    20
        commit_timeout_pct                                             5
        compressed_arc_enabled                                         1
        condense.indirect_commit_entry_delay_ms                        0
        condense.indirect_obsolete_pct                                25
        condense.indirect_vdevs_enable                                 1
        condense.max_obsolete_bytes                           1073741824
        condense.min_mapping_bytes                                131072
        condense_pct                                                 200
        crypt_sessions                                                 0
        dbgmsg_enable                                                  1
        dbgmsg_maxsize                                           4194304
        dbuf.cache_shift                                               5
        dbuf.metadata_cache_max_bytes               18446744073709551615
        dbuf.metadata_cache_shift                                      6
        dbuf_cache.hiwater_pct                                        10
        dbuf_cache.lowater_pct                                        10
        dbuf_cache.max_bytes                        18446744073709551615
        dbuf_state_index                                               0
        ddt_data_is_special                                            1
        deadman.checktime_ms                                       60000
        deadman.enabled                                                1
        deadman.failmode                                            wait
        deadman.synctime_ms                                       600000
        deadman.ziotime_ms                                        300000
        debug                                                          0
        debugflags                                                     0
        dedup.prefetch                                                 0
        default_bs                                                     9
        default_ibs                                                   15
        delay_min_dirty_percent                                       60
        delay_scale                                               500000
        dirty_data_max                                        4294967296
        dirty_data_max_max                                    4294967296
        dirty_data_max_max_percent                                    25
        dirty_data_max_percent                                        10
        dirty_data_sync_percent                                       20
        disable_ivset_guid_check                                       0
        dmu_object_alloc_chunk_shift                                   7
        dmu_offset_next_sync                                           0
        dmu_prefetch_max                                       134217728
        dtl_sm_blksz                                                4096
        flags                                                          0
        fletcher_4_impl [fastest] scalar superscalar superscalar4 sse2 ssse3
        free_bpobj_enabled                                             1
        free_leak_on_eio                                               0
        free_min_time_ms                                            1000
        history_output_max                                       1048576
        immediate_write_sz                                         32768
        initialize_chunk_size                                    1048576
        initialize_value                            16045690984833335022
        keep_log_spacemaps_at_export                                   0
        l2arc.feed_again                                               1
        l2arc.feed_min_ms                                            200
        l2arc.feed_secs                                                1
        l2arc.headroom                                                 2
        l2arc.headroom_boost                                         200
        l2arc.meta_percent                                            33
        l2arc.mfuonly                                                  0
        l2arc.noprefetch                                               1
        l2arc.norw                                                     0
        l2arc.rebuild_blocks_min_l2size                       1073741824
        l2arc.rebuild_enabled                                          0
        l2arc.trim_ahead                                               0
        l2arc.write_boost                                        8388608
        l2arc.write_max                                          8388608
        l2arc_feed_again                                               1
        l2arc_feed_min_ms                                            200
        l2arc_feed_secs                                                1
        l2arc_headroom                                                 2
        l2arc_noprefetch                                               1
        l2arc_norw                                                     0
        l2arc_write_boost                                        8388608
        l2arc_write_max                                          8388608
        l2c_only_size                                                  0
        livelist.condense.new_alloc                                    0
        livelist.condense.sync_cancel                                  0
        livelist.condense.sync_pause                                   0
        livelist.condense.zthr_cancel                                  0
        livelist.condense.zthr_pause                                   0
        livelist.max_entries                                      500000
        livelist.min_percent_shared                                   75
        lua.max_instrlimit                                     100000000
        lua.max_memlimit                                       104857600
        max_async_dedup_frees                                     100000
        max_auto_ashift                                               16
        max_dataset_nesting                                           50
        max_log_walking                                                5
        max_logsm_summary_length                                      10
        max_missing_tvds                                               0
        max_missing_tvds_cachefile                                     2
        max_missing_tvds_scan                                          0
        max_nvlist_src_size                                            0
        max_recordsize                                           1048576
        metaslab.aliquot                                          524288
        metaslab.bias_enabled                                          1
        metaslab.debug_load                                            0
        metaslab.debug_unload                                          0
        metaslab.df_alloc_threshold                               131072
        metaslab.df_free_pct                                           4
        metaslab.df_max_search                                  16777216
        metaslab.df_use_largest_segment                                0
        metaslab.force_ganging                                  16777217
        metaslab.fragmentation_factor_enabled                          1
        metaslab.fragmentation_threshold                              70
        metaslab.lba_weighting_enabled                                 1
        metaslab.load_pct                                             50
        metaslab.max_size_cache_sec                                 3600
        metaslab.mem_limit                                            75
        metaslab.preload_enabled                                       1
        metaslab.preload_limit                                        10
        metaslab.segment_weight_enabled                                1
        metaslab.sm_blksz_no_log                                   16384
        metaslab.sm_blksz_with_log                                131072
        metaslab.switch_threshold                                      2
        metaslab.unload_delay                                         32
        metaslab.unload_delay_ms                                  600000
        mfu_data_esize                                        1861031936
        mfu_ghost_data_esize                                  2537873408
        mfu_ghost_metadata_esize                               897857024
        mfu_ghost_size                                        3435730432
        mfu_metadata_esize                                      33828864
        mfu_size                                              2202412032
        mg.fragmentation_threshold                                    95
        mg.noalloc_threshold                                           0
        min_auto_ashift                                                9
        min_metaslabs_to_flush                                         1
        mru_data_esize                                        5718893056
        mru_ghost_data_esize                                  1717017600
        mru_ghost_metadata_esize                              1878866432
        mru_ghost_size                                        3595884032
        mru_metadata_esize                                      52778496
        mru_size                                              7154395648
        multihost.fail_intervals                                      10
        multihost.history                                              0
        multihost.import_intervals                                    20
        multihost.interval                                          1000
        multilist_num_sublists                                         0
        no_scrub_io                                                    0
        no_scrub_prefetch                                              0
        nocacheflush                                                   0
        nopwrite_enabled                                               1
        obsolete_min_time_ms                                         500
        pd_bytes_max                                            52428800
        per_txg_dirty_frees_percent                                    5
        prefetch.array_rd_sz                                     1048576
        prefetch.disable                                               0
        prefetch.max_distance                                    8388608
        prefetch.max_idistance                                  67108864
        prefetch.max_streams                                           8
        prefetch.min_sec_reap                                          2
        read_history                                                   0
        read_history_hits                                              0
        rebuild_max_segment                                      1048576
        reconstruct.indirect_combinations_max                       4096
        recover                                                        0
        recv.queue_ff                                                 20
        recv.queue_length                                       16777216
        recv.write_batch_size                                    1048576
        reference_tracking_enable                                      0
        removal_suspend_progress                                       0
        remove_max_segment                                      16777216
        resilver_disable_defer                                         0
        resilver_min_time_ms                                        3000
        scan_checkpoint_intval                                      7200
        scan_fill_weight                                               3
        scan_ignore_errors                                             0
        scan_issue_strategy                                            0
        scan_legacy                                                    0
        scan_max_ext_gap                                         2097152
        scan_mem_lim_fact                                             20
        scan_mem_lim_soft_fact                                        20
        scan_strict_mem_lim                                            0
        scan_suspend_progress                                          0
        scan_vdev_limit                                          4194304
        scrub_min_time_ms                                           1000
        send.corrupt_data                                              0
        send.no_prefetch_queue_ff                                     20
        send.no_prefetch_queue_length                            1048576
        send.override_estimate_recordsize                              0
        send.queue_ff                                                 20
        send.queue_length                                       16777216
        send.unmodified_spill_blocks                                   1
        send_holes_without_birth_time                                  1
        slow_io_events_per_second                                     20
        spa.asize_inflation                                           24
        spa.discard_memory_limit                                16777216
        spa.load_print_vdev_tree                                       0
        spa.load_verify_data                                           1
        spa.load_verify_metadata                                       1
        spa.load_verify_shift                                          4
        spa.slop_shift                                                 5
        space_map_ibs                                                 14
        special_class_metadata_reserve_pct                            25
        standard_sm_blksz                                         131072
        super_owner                                                    0
        sync_pass_deferred_free                                        2
        sync_pass_dont_compress                                        8
        sync_pass_rewrite                                              2
        sync_taskq_batch_pct                                          75
        top_maxinflight                                             1000
        traverse_indirect_prefetch_limit                              32
        trim.extent_bytes_max                                  134217728
        trim.extent_bytes_min                                      32768
        trim.metaslab_skip                                             0
        trim.queue_limit                                              10
        trim.txg_batch                                                32
        txg.history                                                  100
        txg.timeout                                                    5
        unflushed_log_block_max                                   262144
        unflushed_log_block_min                                     1000
        unflushed_log_block_pct                                      400
        unflushed_max_mem_amt                                 1073741824
        unflushed_max_mem_ppm                                       1000
        user_indirect_is_special                                       1
        validate_skip                                                  0
        vdev.aggregate_trim                                            0
        vdev.aggregation_limit                                   1048576
        vdev.aggregation_limit_non_rotating                       131072
        vdev.async_read_max_active                                     3
        vdev.async_read_min_active                                     1
        vdev.async_write_active_max_dirty_percent                     60
        vdev.async_write_active_min_dirty_percent                     30
        vdev.async_write_max_active                                    5
        vdev.async_write_min_active                                    1
        vdev.bio_delete_disable                                        0
        vdev.bio_flush_disable                                         0
        vdev.cache_bshift                                             16
        vdev.cache_max                                             16384
        vdev.cache_size                                                0
        vdev.def_queue_depth                                          32
        vdev.default_ms_count                                        200
        vdev.default_ms_shift                                         29
        vdev.file.logical_ashift                                       9
        vdev.file.physical_ashift                                      9
        vdev.initializing_max_active                                   1
        vdev.initializing_min_active                                   1
        vdev.max_active                                             1000
        vdev.max_auto_ashift                                          16
        vdev.min_auto_ashift                                           9
        vdev.min_ms_count                                             16
        vdev.mirror.non_rotating_inc                                   0
        vdev.mirror.non_rotating_seek_inc                              1
        vdev.mirror.rotating_inc                                       0
        vdev.mirror.rotating_seek_inc                                  5
        vdev.mirror.rotating_seek_offset                         1048576
        vdev.ms_count_limit                                       131072
        vdev.nia_credit                                                5
        vdev.nia_delay                                                 5
        vdev.queue_depth_pct                                        1000
        vdev.read_gap_limit                                        32768
        vdev.rebuild_max_active                                        3
        vdev.rebuild_min_active                                        1
        vdev.removal_ignore_errors                                     0
        vdev.removal_max_active                                        2
        vdev.removal_max_span                                      32768
        vdev.removal_min_active                                        1
        vdev.removal_suspend_progress                                  0
        vdev.remove_max_segment                                 16777216
        vdev.scrub_max_active                                          3
        vdev.scrub_min_active                                          1
        vdev.sync_read_max_active                                     10
        vdev.sync_read_min_active                                     10
        vdev.sync_write_max_active                                    10
        vdev.sync_write_min_active                                    10
        vdev.trim_max_active                                           2
        vdev.trim_min_active                                           1
        vdev.validate_skip                                             0
        vdev.write_gap_limit                                        4096
        version.acl                                                    1
        version.ioctl                                                 15
        version.module v2021052700-zfs_b4f504202869094d805defb3c5d7938116ba1226
        version.spa                                                 5000
        version.zpl                                                    5
        vnops.read_chunk_size                                    1048576
        vol.mode                                                       2
        vol.recursive                                                  0
        vol.unmap_enabled                                              1
        zap_iterate_prefetch                                           1
        zevent.cols                                                   80
        zevent.console                                                 0
        zevent.len_max                                               512
        zevent.retain_expire_secs                                    900
        zevent.retain_max                                           2000
        zfetch.max_distance                                      8388608
        zfetch.max_idistance                                    67108864
        zil.clean_taskq_maxalloc                                 1048576
        zil.clean_taskq_minalloc                                    1024
        zil.clean_taskq_nthr_pct                                     100
        zil.maxblocksize                                          131072
        zil.nocacheflush                                               0
        zil.replay_disable                                             0
        zil.slog_bulk                                             786432
        zio.deadman_log_all                                            0
        zio.dva_throttle_enabled                                       1
        zio.exclude_metadata                                           0
        zio.requeue_io_start_cut_in_line                               1
        zio.slow_io_ms                                             30000
        zio.taskq_batch_pct                                           80
        zio.taskq_batch_tpq                                            0
        zio.use_uma                                                    1

VDEV cache disabled, skipping section

ZIL committed transactions:                                         4.3M
        Commit requests:                                           94.2k
        Flushes to stable storage:                                 94.2k
        Transactions to SLOG storage pool:            0 Bytes          0
        Transactions to non-SLOG storage pool:       83.9 GiB     765.3k

 

[revengineer]

I am using Truenas 12, so I am not sure whether I should be using vfs.zfs.arc_max or vfs.zfs.arc.max.

 

[revengineer]

So I tried both vfs.zfs.arc_max or vfs.zfs.arc.max and tried loading each as "loader" and "sysctl" tunable. Non of these combinations work. In each case arc_summary shows a max arc size of 10G. The only way to change this is to issue the command "sysctl vfs.zfs.arc_max="32212254720". I am either too dumb or there is a bug; I am hoping its the former. Enough for tonight, help appreciated.

 

[revengineer]

I cannot imagine that I am the only one in this boat. Is there really no advice?

Perhaps I do need to go the route of a bug report.

 

[revengineer]

So, a while ago, I filed a bug report on this here but continued to dig into the issue. Today I finally found the underlying issue.
Here is what I did:

1. I disabled the autostart of VMs and rebooted, et voila the arc size was properly set to 30G.
2. I then manually started my first VM, which requires 8G memory, and the arc size was reduced by the same amount to 22G.
3. I started the second VM, which requires 4G, and arc size went to 18G.
4. I started the final VM, which requires 8G, and arc size went to the 10G value I have been reporting.

So conclusion is that bhyve interacts with ZFS but does not do so very intelligently because with 90G total ECC RAM, I can easily hold 30G in VMs AND a 30G ARC in memory.

 

[NugentS]

So what you are saying is that bhyve removes RAM from the ARC (which you have set to 30GB) and not from the total RAM of 90GB

I would suggest that that is non-intuitive. I think you need to remove that tunable and just carefully count the VM memory

 

[revengineer]

So what you are saying is that bhyve removes RAM from the ARC (which you have set to 30GB) and not from the total RAM of 90GB

I would suggest that that is non-intuitive. I think you need to remove that tunable and just carefully count the VM memory

Correct. The tunable vfs.zfs.arc.max is set to 30G. After 3 VMs autostart at boot (together requiring 20G of RAM) the command arc_summary shows that arc.max is reduced to 10G. So VMs seem to be taking RAM from ARC rather than just using the extra 60G floating around.

Removing the tunable is possibly an option but I have run into memory trouble without the tunable on FreeNAS 11.3. I will wait for a response to the JIRA ticket to hear what they suggest as well. In the meantime, I set the ARC size by sysctl command after boot. As long as I do not reboot the VMs this should work.

 

[revengineer]

So, after working through the bug ticket, there are two issues here:

1. The system always reduces the ARC size to get memory for a VM. I filed a suggestion to change the logic to use free memory if available instead of reducing ARC size. This is suggestion NAS-112188.
2. The system does not increase the ARC size again after a VM is shutdown from the VM itself (which I do all the time). It does work if the VM is turned off from the TrueNAS GUI. This apparently has been been fixed in NAS-111491. However, although I reported the issue for TrueNAS Core, the fix seems to only apply to SCALE. This is freaking maddening because for over a month I communicated on the ticket and ran numerous tests, all effort apparently with ZERO return. If this is the way this project works, I will not donate my time for this in the future; I am just too busy and need to choose these contributions carefully.

Cheers

 

[SMnasMAN]

sysctl vfs.zfs.arc_max="32212254720"

thank you very much for taking the time to write this thread (and work with IXsys on the bug/suggestion). Your thread (and time) helped me save alot of time. I do hope that ixsys values your time and contribution.