git: kernel - Implement a more comprehensive low-memory deadlock solution

Matthew Dillon dillon at
Thu Aug 24 22:32:41 PDT 2017

commit c3feb36a35386093f8f28e8a125eab625bf825d3
Author: Matthew Dillon <dillon at>
Date:   Thu Aug 24 22:25:02 2017 -0700

    kernel - Implement a more comprehensive low-memory deadlock solution
    * Low memory deadlocks occur when the pageout daemon needs memory
      resources that the kernel cannot provide.  The pageout daemon itself
      is given more of an emergency reserve than other threads, but this
      is not sufficient.
      The complex nature of VFS's, particularly sohpisticated filesystems,
      can create situations where the pageout daemon gets stuck on locks
      held by filesystem related threads which themselves are stuck waiting
      for memory.
    * Try to solve this problem by having two kernel pageout daemons.  The
      main daemon works as usual.  The second daemon monitors the first
      one looking for stalls and takes over if it detects one.
      The second daemon will skip problematic vnodes and only pageout
      anonymous memory.  At some point the main daemon will unstick and
      be able to resume normal operating.
    * Paging anonymous memory is far less resource intensive than paging
      through a vnode, so it is far more likely that the emergency daemon
      will be able to make progress to resolve the low memory situation
      when the primary daemon gets stuck.

Summary of changes:
 sys/vm/vm_pageout.c | 201 ++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 181 insertions(+), 20 deletions(-)

DragonFly BSD source repository

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