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Prefetch on deadlists merge. #14402

Merged
merged 1 commit into from
Jan 25, 2023
Merged

Prefetch on deadlists merge. #14402

merged 1 commit into from
Jan 25, 2023

Commits on Jan 21, 2023

  1. Prefetch on deadlists merge. 

    During snapshot deletion ZFS may issue several reads for each deadlist
to merge them into next snapshot's or pool's bpobj.  Number of the dead
lists increases with number of snapshots.  On HDD pools it may take
significant time during which sync thread is blocked.

This patch introduces prescient prefetch of required blocks for up to
128 deadlists ahead.  Tests show reduction of time required to delete
dataset with 720 snapshots with randomly overwritten file on wide HDD
pool from 75-85 to 22-28 seconds.

Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
    @amotin
    amotin committed Jan 21, 2023
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