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Diffstat (limited to 'man')
| -rw-r--r-- | man/man4/zfs.4 | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/man/man4/zfs.4 b/man/man4/zfs.4 index 45b6c338a..aae3d7dfb 100644 --- a/man/man4/zfs.4 +++ b/man/man4/zfs.4 @@ -974,6 +974,88 @@ milliseconds until the operation completes. .It Sy zfs_dedup_prefetch Ns = Ns Sy 0 Ns | Ns 1 Pq int Enable prefetching dedup-ed blocks which are going to be freed. . +.It Sy zfs_dedup_log_flush_passes_max Ns = Ns Sy 8 Ns Pq uint +Maximum number of dedup log flush passes (iterations) each transaction. +.Pp +At the start of each transaction, OpenZFS will estimate how many entries it +needs to flush out to keep up with the change rate, taking the amount and time +taken to flush on previous txgs into account (see +.Sy zfs_dedup_log_flush_flow_rate_txgs ) . +It will spread this amount into a number of passes. +At each pass, it will use the amount already flushed and the total time taken +by flushing and by other IO to recompute how much it should do for the remainder +of the txg. +.Pp +Reducing the max number of passes will make flushing more aggressive, flushing +out more entries on each pass. +This can be faster, but also more likely to compete with other IO. +Increasing the max number of passes will put fewer entries onto each pass, +keeping the overhead of dedup changes to a minimum but possibly causing a large +number of changes to be dumped on the last pass, which can blow out the txg +sync time beyond +.Sy zfs_txg_timeout . +. +.It Sy zfs_dedup_log_flush_min_time_ms Ns = Ns Sy 1000 Ns Pq uint +Minimum time to spend on dedup log flush each transaction. +.Pp +At least this long will be spent flushing dedup log entries each transaction, +up to +.Sy zfs_txg_timeout . +This occurs even if doing so would delay the transaction, that is, other IO +completes under this time. +. +.It Sy zfs_dedup_log_flush_entries_min Ns = Ns Sy 1000 Ns Pq uint +Flush at least this many entries each transaction. +.Pp +OpenZFS will estimate how many entries it needs to flush each transaction to +keep up with the ingest rate (see +.Sy zfs_dedup_log_flush_flow_rate_txgs ) . +This sets the minimum for that estimate. +Raising it can force OpenZFS to flush more aggressively, keeping the log small +and so reducing pool import times, but can make it less able to back off if +log flushing would compete with other IO too much. +. +.It Sy zfs_dedup_log_flush_flow_rate_txgs Ns = Ns Sy 10 Ns Pq uint +Number of transactions to use to compute the flow rate. +.Pp +OpenZFS will estimate how many entries it needs to flush each transaction by +monitoring the number of entries changed (ingest rate), number of entries +flushed (flush rate) and time spent flushing (flush time rate) and combining +these into an overall "flow rate". +It will use an exponential weighted moving average over some number of recent +transactions to compute these rates. +This sets the number of transactions to compute these averages over. +Setting it higher can help to smooth out the flow rate in the face of spiky +workloads, but will take longer for the flow rate to adjust to a sustained +change in the ingress rate. +. +.It Sy zfs_dedup_log_txg_max Ns = Ns Sy 8 Ns Pq uint +Max transactions to before starting to flush dedup logs. +.Pp +OpenZFS maintains two dedup logs, one receiving new changes, one flushing. +If there is nothing to flush, it will accumulate changes for no more than this +many transactions before switching the logs and starting to flush entries out. +. +.It Sy zfs_dedup_log_mem_max Ns = Ns Sy 0 Ns Pq u64 +Max memory to use for dedup logs. +.Pp +OpenZFS will spend no more than this much memory on maintaining the in-memory +dedup log. +Flushing will begin when around half this amount is being spent on logs. +The default value of +.Sy 0 +will cause it to be set by +.Sy zfs_dedup_log_mem_max_percent +instead. +. +.It Sy zfs_dedup_log_mem_max_percent Ns = Ns Sy 1 Ns % Pq uint +Max memory to use for dedup logs, as a percentage of total memory. +.Pp +If +.Sy zfs_dedup_log_mem_max +is not set, it will be initialised as a percentage of the total memory in the +system. +. .It Sy zfs_delay_min_dirty_percent Ns = Ns Sy 60 Ns % Pq uint Start to delay each transaction once there is this amount of dirty data, expressed as a percentage of |