memory overhead of rtems regions

[Matthew J Fletcher]

Hi,

Reading the documentation for rtems regions is a bit vague about the
overhead of the lists that behind the scenes manage the blocks. Its quite
possible i am not fully understanding the operation. I have a call sequence
as follows.

rtems_region_create( length = 19800, page_size = 128 )
  rtems_region_get_segment( size = 160 )
    rtems_message_queue_create ( count = 160, max_size =2 )
  rtems_region_get_segment( size = 400 )
    rtems_message_queue_create ( count = 400, max_size =2 )
  rtems_region_get_segment( size = 1600 )
    rtems_message_queue_create ( count = 1600, max_size =2 )
  rtems_region_get_segment( size = 40 )
    rtems_message_queue_create ( count = 40, max_size =2 )
  rtems_region_get_segment( size = 4000 )
    rtems_message_queue_create ( count = 4000, max_size =2 )
  rtems_region_get_segment( size = 40 )
    rtems_message_queue_create ( count = 40, max_size =2 )
  rtems_region_get_segment( size = 40 )
    rtems_message_queue_create ( count = 40, max_size =2 )
  rtems_region_get_segment( size = 40 )
    rtems_message_queue_create ( count = 40, max_size =2 )
  rtems_region_get_segment( size = 40 )
    rtems_message_queue_create ( count = 40, max_size =2 )
  rtems_region_get_segment( size = 120 )
    rtems_message_queue_create ( count = 120, max_size =2 )
  rtems_region_get_segment( size = 400 )
    rtems_message_queue_create ( count = 400, max_size =2 )
  rtems_region_get_segment( size = 400 )
    rtems_message_queue_create ( count = 400, max_size =2 )
  rtems_region_get_segment( size = 2000 ) // total size upto here 7320
    rtems_message_queue_create ( count = 2000, max_size =2 )
    // returns RTEMS_UNSATISFIED - unable to allocate message buffers here

I dont fully understand why RTEMS_UNSATISFIED is being returned from the
queue_create(), is there really a 50%+ overhead in managing 128 byte pages
? out of a 19800 length.

I am presuming that the RTEMS_UNSATISFIED is because of the region size,
but i could be wrong about that.


regards
---
Matthew J Fletcher
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