Commits on Mar 29, 2024

1. L2ARC: Relax locking during write …

   Previous code held ARC state sublist lock throughout all L2ARC
   write process, which included number of allocations and even ZIO
   issues.  Being blocked in any of those places the code could also
   block ARC eviction, that could cause OOM activation or even dead-
   lock if system is low on memory or one is too fragmented.
   
   Fix it by dropping the lock as soon as we see a block eligible
   for L2ARC writing and pick it up later using earlier inserted
   marker.  While there, also reduce scope of hash lock, moving
   ZIO allocation and other operations not requiring header access
   out of it.  All operations requiring header access move under
   hash lock, since L2_WRITING flag does not prevent header eviction
   only transition to arc_l2c_only state with L1 header.
   
   To be able to manipulate sublist lock and marker as needed add few
   more multilist functions and modify one.
   
   Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
   Sponsored by:	iXsystems, Inc.

   

   amotin committed Mar 29, 2024
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