Method and system for efficiently using buffer space

An adapter that receives a protocol data unit (PDU) from a network device, comprising:

• a local memory for the adapter for initially storing the PDU after the PDU is received from the network device;
• and
• a processor that processes the received PDU and sends the PDU to the host system memory via a direct memory access channel (DMA) managed by a DMA engine;
• wherein the DMA engine maintains a pool of small buffers and a pool of large buffers, for intermediate storage of the PDU before the PDU is transferred to the host system memory, and the DMA engine:
• (a) compares a size of the PDU with the size of a small buffer and if the PDU fits in the small buffer, then the PDU is placed in the small buffer;
• and (b) if the PDU size is greater than the small buffer size, compares the size of the PDU with a large buffer size and if the PDU size is less than the large buffer size then the PDU is placed in the large buffer;
• and (c) if the PDU size is greater than a large buffer size, then the PDU is placed in more than one large buffer and a pointer to a list of large buffers storing the PDU is placed in the small buffer;
• wherein the host system is notified whether the small buffer, the large buffer or the more than one large buffer is used for intermediate storage.

A system for transferring protocol data units (“PDUs”), comprising:

• a host system with a host system memory coupled to a network via a network adapter that receives a PDU from the network;
• wherein the network adapter includes:
• a local memory that initially stores the PDU after the PDU is received from the network system;
• and
• a processor that processes the received PDU and sends the PDU to the host system memory via a direct memory access channel (DMA) managed by a DMA engine;
• wherein the DMA engine maintains a pool of small buffers and a pool of large buffers for intermediate storage of the PDU before the PDU is transferred to the host system memory, and the DMA engine:
• (a) compares a size of the PDU with the size of a small buffer and if the PDU fits in the small buffer, then the PDU is placed in the small buffer;
• and (b) if the PDU size is greater than the small buffer size, then compares the size of the PDU with a large buffer size, and if the PDU size is less than the large buffer size then the PDU is placed in the large buffer;
• and (c) if the PDU size is greater than a large buffer size, then the PDU is placed in more than one large buffer and a pointer to a list of the large buffers storing the PDU is placed in the small buffer;
• wherein the host system is notified whether the small buffer, the large buffer or the more than one large buffer is used for intermediate storage.