[LU-18939] readahead parameters should allow percentage with sysfs_memparse_total()

• Type: Improvement
• Resolution: Unresolved
• Priority: Minor
• Affects Version/s: Lustre 2.14.0, Lustre 2.16.1
• Labels: easy readahead tuning
• Severity: 3
• Assignee: Patrick Farrell
• Reporter: Andreas Dilger

Description

The llite.*.max_read_ahead_mb, llite.*.max_read_ahead_per_file_mb, and llite.*.max_read_ahead_whole_mb parameters should be updated to allow being set as a percentage of the total RAM size, so that it is possible to set permanent parameters like "llite.*.max_read_ahead_mb=25%" and "llite.*.max_read_ahead_per_file_mb=5%" that are useful for a variety of different clients.

This can be achieved by using sysfs_memparse_total() to parse the input with a trailing '%' unit, as in ll_max_cached_mb_seq_write(). It probably does not make sense to allow setting the readahead larger than cfs_totalram_pages()/2, as done today, but it should be possible to set it at 50%.

Issue Links

• is related to: LU-17030 allow setting max_cached_mb with %