[LU-18634] add non-page tunable max_mb_per_rpc parameter

• Type: Improvement
• Resolution: Duplicate
• Priority: Minor
• Labels: easy
• Severity: 3
• Assignee: WC Triage
• Reporter: Andreas Dilger

Description

It would be useful to add a new "{osc,mdc}.*.max_mb_per_rpc" tunable parameter to dissociate the RPC size from the client page size as implied by "{osc,mdc}.*.max_pages_per_rpc". While it is already to specify "max_pages" with a unit like "4M" or "16M" to avoid issues with page sizes, this is still printed as a number of pages, and values without units are assumed to be pages. It would be better to have a dedicated parameter for specifying the RPC size, and (very) slowly deprecate max_pages_per_rpc in the future.

The max_mb_per_rpc parameter should internally convert the specified parameter to pages and still modify the same cl_max_pages_per_rpc variable, the same as max_pages_per_rpc does today, but provides a more consistent userspace interface for doing so.

The parameter should accept units and fractional parameters (e.g. 0.5M and 64k), which is already handled by sysfs_memparse(), so that it is possible to specify RPC sizes smaller than 1MiB in the rare case this is needed.

Issue Links

• duplicates: LU-18635 add non-page tunable max_mb_per_rpc_read/write parameters