[LU-15550] WBC: retry the batched RPC when the reply buffer is overflowed

• Type: Improvement
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.16.0
• Assignee: Qian Yingjin
• Reporter: Qian Yingjin

Description

Before send the batched RPC, we have no idea about the actual reply buffer size.
The reply buffer size the client prepared may be smaller than the reply buffer in need, we can grow the reply buffer properly.

But when the needed reply buffer size is larger than BUT_MAXREPSIZE (1000 * 1024), the server will return -EOVERFLOW error code. At this time, the server only executed the partial sub requests in the batched RPC. The overflowed sub requests will not be executed.

Thus the client needs a retry mechanism: when found that the reply buffer overflowed, the client will rebuild the batched RPC for the sub requests that not executed on the server, and send to the server to re-executed them again.

Issue Links

• is related to: LU-16907 sanity test_123f: crashed MDS with Max IOV exceeded: 257 should be < 256
• is related to: LU-14139 batched statahead processing
• is related to: LU-15975 Statahead_V1 Features