[LU-11449] osc: send RPCs with random i/o

• Type: Bug
• Resolution: Not a Bug
• Priority: Major
• Labels: patch
• Severity: 3
• Assignee: Patrick Farrell (Inactive)
• Reporter: Patrick Farrell (Inactive)

Description

LU-8515 modified osc_makes_rpc to remove a check which sent RPCs once the total number of pages == max_pages_per_rpc.  This fixed an issue with > 1 writer per stripe where smaller, fragmented RPCs would be sent instead of full size RPCs.

However, it introduced a different issue with small random writes, particularly when sparse.  Because small random writes will (in the large file/sparse case) not make complete, contiguous extents, no RPCs will be sent until the max_dirty_mb or grant limit is hit.

This means that in the small-random-sparse write case not enough RPCs will be sent.

The solution is to add an additional check for greater than max_pages_per_rpc pages.  Details in patch.

Issue Links

• is related to: LU-10239 Lustre crash (client): The first extent to be fit in a RPC contains 17 chunks, which is over the limit 16.
• is related to: LU-11526 Support 64MB I/O RPC

Comments

[Patrick Farrell (Inactive)]

Existing behavior turns out to be OK.

[Patrick Farrell (Inactive)]

Note from Gerrit, where patch is to be abandoned:

The theory of i/o performance I had in mind when I created this appears to be wrong... Basically, it's reasonable to wait for the cache limit to be hit, and it doesn't take long. This seems to be an unnecessary optimization.