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When displaying the current memory usage on Juniper MX systems (running JunOS 21.4, in case it should matter), I do see an entry for Laundry. For example:

> show system processes extensive
Mem: 13330M Active, 430M Inact, 13918M Laundry, 3198M Wired, 1374M Buf, 904M Free
(...)

Other Juniper systems like the EX and QFX switches do not show this field under show system processes extensive. Junipers own documentation for memory management also does not mention Laundry anywhere, although it explains all the other fields in detail.

What is this "Laundry"-memory, and is it safe to assume it can be released by the system if required for something else? (Or is the above system close to running out of memory?)

1 Answer 1

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Junos OS is based on FreeBSD:

Laundry

  • Queue for managing dirty inactive pages, which must be cleaned ("laundered") before they can be reused
  • Managed by a separate thread, the laundry thread, instead of the page daemon
  • Laundry thread launders a small number of pages to balance the inactive and laundry queues
  • Frequency of laundering depends on:
    • How many clean pages the page daemon is freeing; more frees contributes to a higher frequency of laundering
    • The size of the laundry queue relative to the inactive queue; if the laundry queue is growing, we will launder more frequently
  • Pages are scanned by the laundry thread (starting from the head of the queue): Pages which have been referenced are moved back to the active queue or the tail of the laundry queue Dirty pages are laundered and then moved close to the head of the inactive queue

https://wiki.freebsd.org/Memory

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