Commits on Jun 22, 2022

1. Several sorted scrub optimizations. …

    - Reduce size and comparison complexity of q_exts_by_size B-tree.
   Previous code used two 64-bit divisions and many other operations to
   compare two B-tree elements.  It created enormous overhead.  This
   implementation moves the math to the upper level and stores the score
   in the B-tree elements themselves.  Since all that we need to store in
   that B-tree is the extent score and offset, those can fit into single
   8 byte value instead of 24 bytes of q_exts_by_addr element and can be
   compared with single operation.
    - Better decouple secondary tree logic from main range_tree by moving
   rt_btree_ops and related functions into dsl_scan.c as ext_size_ops.
   Those functions are very small to worry about the code duplication and
   range_tree does not need to know details such as rt_btree_compare.
    - Instead of accounting number of pending bytes per pool, that needs
   atomic on global variable per block, account the number of non-empty
   per-vdev queues, that change much more rarely.
    - When extent scan is interrupted by TXG end, continue it in the next
   TXG instead of selecting next best extent.  It allows to avoid leaving
   one truncated (and so likely not the best any more) extent each TXG.
   
   On top of some other optimizations this saves about 1.5 minutes out of
   10 to scrub pool of 12 SSDs, storing 1.5TB of 4KB zvol blocks.
   
   Signed-off-by: Alexander Motin <mav@FreeBSD.org>
   Sponsored-By: iXsystems, Inc.

   

   amotin committed Jun 22, 2022
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