There is no upper limit on the number of messages buffer for a sleep end device.

[jinpeng1989]

The timeout of our sleep-end-device is 1800 seconds. When a SED leaves the network. All the messages send to it will be buffer until
timeout expired. The disconnected device may have consumed all of the messages buffer, other devices cannot work properly.

To Reproduce Information to reproduce the behavior, including:

1. Git commit id: 3a98779
   ot-br-posix/2022-06-02-3a98779-2; POSIX; Feb 15 2021 15:22:37
2. IEEE 802.15.4 hardware platform: SL-OPENTHREAD/2.1.0.0_GitHub-8f92d2dc8_v1; EFR32; Jul 19 2022 14:18:51
3. Build steps
   Join a SED(timeout=1800 second). Power off SED, than send message to this SED. The otbr-agent buffer will continue to decrease until it runs out.

Expected behavior A clear and concise description of what you expected to happen.
There is a maximum of messages buffer for a given sleep end device. Messages exceeding the upper limit can be dropped.

[jwhui]

What you are observing is expected. If OpenThread has buffers available, it will utilize them. However, if those buffers are needed at a later time, it can reclaim them by evicting already-buffered messages.

See MessagePool::NewBuffer() call to ReclaimBuffers():

openthread/src/core/common/message.cpp

Line 122 in cba1beb

SuccessOrExit(ReclaimBuffers(aPriority));

Which calls MeshForwarder::EvictMessage():

openthread/src/core/thread/mesh_forwarder_ftd.cpp

Line 205 in cba1beb

Error MeshForwarder::EvictMessage(Message::Priority aPriority)

As a result, just because the router is buffering messages for a child, that should not prevent it from buffering other messages that it needs to forward later on.

[jinpeng1989]

So only when there is no buffer can be reclaim means that no available message buffer. If the level of this log can be improved?

If define OPENTHREAD_CONFIG_DEFAULT_SED_DATAGRAM_COUNT to 8. Whether otbr-agent can guarantee 8 buffer for a given SED? Will the newest or the oldest be dropped?

[jwhui]

So only when there is no buffer can be reclaim means that no available message buffer. If the level of this log can be improved?

If no buffers can be reclaimed allocation will fail. Can you point to a specific log line that you are referring to?

If define OPENTHREAD_CONFIG_DEFAULT_SED_DATAGRAM_COUNT to 8. Whether otbr-agent can guarantee 8 buffer for a given SED? Will the newest or the oldest be dropped?

The current implementation will evict the message with lowest priority. If multiple messages exist at the lowest priority, it will evict the oldest one. See implementation at:

openthread/src/core/thread/mesh_forwarder_ftd.cpp

Line 205 in cba1beb

Error MeshForwarder::EvictMessage(Message::Priority aPriority)

[jinpeng1989]

The free number is greater than total in our test environment. Please help to check.

[jwhui]

Number of free buffers should not be greater than number of total buffers.

Number of total buffers should be static - see implementation:

openthread/src/core/common/message.cpp

Line 181 in ba00622

uint16_t MessagePool::GetTotalBufferCount(void) const

Your original post showed 16383 total buffers. However, the post immediately above shows 8192 buffers. Are these difference devices? If so, can you provide more information on how their configurations differ?

[jinpeng1989]

These are two different devices. The total buffers of the first device is 16383. The second device is 8192. Only this configurations differ.

[jinpeng1989]

If no buffers can be reclaimed allocation will fail. Can you point to a specific log line that you are referring to?

[https://github.com/openthread/openthread/blob/main/src/core/common/message.cpp#L134](url)

[jwhui]

This log line:

openthread/src/core/common/message.cpp

Line 134 in ba00622

LogInfo("No available message buffer");

Indicates that ReclaimBuffers() could not provide any free buffers.