Application performance dropped after upgrade to RHEL 8.5

Issue

• After updating the system to RHEL 8.5 (kernel-4.18.0-348) the application is showing significant performance drop.

  The application vendor found that in older kernel, the read_ahead_kb value was 128 KB:

  $ cat /sys/block/sdb/queue/read_ahead_kb
  128
  

  But after update to 8.5 kernel, the system is using 32 MB read_ahead_kb value:

  $ cat /sys/block/sdb/queue/read_ahead_kb
  32768
  

  Changing the read_ahead_kb count back to 128 KB fixes the performance issue.

• We would like to understand why the newer kernel is setting different read_ahead_kb value?