GM-2, send/recv and size of messages

Hi,

I am working with GM-2. After reading the docu:
http://www.myri.com/scs/GM-2/doc/html/Receiving_Messages.html#receiving
it says that the size of the incomming message and the size of the buffer provided for receiving must match EXACTLY.
This is very strange and uncomfortable.
The I look in the MPICH source, which is based on GM.
In file:
mpich-1.2.5..10/mpid/ch_gm/gmpi.h
in line 72 
#define GMPI_PKT_GM_SIZE 30
this is used in gmpi_priv.c in 
gmpi_send_packet() for gm_send_with_callback()
that means the a message of the size 30 (2^30 byte) will be send?
Do I need to gm_dma_malloc therefor 2^30 bytes of mem? That is one GiB of mem....
And what about the length of the message to send. Can it differ from the size (size = log2(length + 8)).

Any help out there?

Thomas.



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