net/rds: Reduce memory footprint in rds_sendmsg

net/rds: Reduce memory footprint in rds_sendmsg

Orabug: 26151323

8K + 256 (8448B) is an important message size for the RDBMS workload. Since
Infiniband supports scatter-gather in hardware, there is no reason to
fragment each RDS message into PAGE_SIZE work requests. Hence, RDS fragment
sizes up to 16K has been introduced.

Fixes: 23f90cccfba4 ("RDS: fix the sg allocation based on actual msg sz")
Previous behavior was allocating a contiguous memory buffer, corresponding
to the size of the RDS message. Although this was functional correct, it
introduced hard pressure on the memory allocation system, which was
not needed.

This commit fixes the drawback introduced by only allocating
the buffer according to RDS_MAX_FRAG_SIZE.

Orabug: 26350949

Signed-off-by: Wei Lin Guay <wei.lin.guay@oracle.com>
Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com>
Acked-by: Joe Jin <joe.jin@oracle.com>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Tested-by: John Sobecki <john.sobecki@oracle.com>