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Description of problem:

mem.vmstat.drop_pagecache & mem.vmstat.drop_slab metric values are always zero though the /proc/vmstat reflects them properly. 

Version-Release number of selected component (if applicable):
pcp-5.0.2-5.el8.x86_64

How reproducible:


Steps to Reproduce:
1. drop the cache couple of times 
 
$echo 3 > /proc/sys/vm/drop_caches
$ echo 3 > /proc/sys/vm/drop_caches
$ echo 2 > /proc/sys/vm/drop_caches
$ echo 2 > /proc/sys/vm/drop_caches
$ echo 1 > /proc/sys/vm/drop_caches

2. The /proc/vmstat has refelected the values: 

$ cat /proc/vmstat | grep -i drop
  drop_pagecache 2
  drop_slab 2

3. but PCP is not able to read it properly. Its always zero: 

$ pmrep mem.vmstat.drop_pagecache
  m.v.drop_pagecache
  count/s
  N/A
  0.000
  0.000
  0.000
  0.000
  0.000

$ pmrep mem.vmstat.drop_slab
  m.v.drop_slab
  count/s
  N/A
  0.000
  0.000
  ^C


Actual results:

mem.vmstat.drop_pagecache & mem.vmstat.drop_pagecache metric values are always zero

Expected results:

They should reflect the real time values. 

Additional info:

Will be resolved via rebase in 8.4 - marking as dup to simplify tracking.

*** This bug has been marked as a duplicate of bug 1854035 ***

*** This bug has been marked as a duplicate of bug 1854035 ***