Observations on virtual memory operations

[doug]

On Wed, 30 Dec 2020, Steve O'Hara-Smith wrote:

> On Wed, 30 Dec 2020 01:03:05 +0000 (UTC)
> doug at safeport.com wrote:
>
>> I do not seem to be able to say clearly enough, there is no memory
>> problem, the is a problem with the paging subsystem filling up swapspace.
>
> 	Are you using tmpfs or swap backed md ?
>
Neither:
    swapctl -l
    Device:       1024-blocks     Used:
    /dev/aacd0p3    4194304   1857780

from vmstat:
    procs  memory       page                      faults         cpu
    r b w  avm   fre   flt  re  pi  po    fr   sr   in    sy    cs us sy id
    2 0 16  13G  1.7G  2557   0   0   0  3044  435  509  5523   875  7  1 93
    0 0 16  14G  1.5G  8582   0   0   0  7366  428  491  6410   731  6  1 92
    0 0 16  14G  1.5G  2945   0   0   0  2934  480  511  4313   780  6  1 93
    0 0 16  14G  1.6G  3795   0   0   0  3950  457  434  4910   716  5  1 94
    1 0 16  14G  1.6G   589   0   0   0  1128  431  777  2128  1481  2  1 98
    2 0 16  14G  1.6G  3273   0   1   0  3329  446  715  5871  1266  5  1 94

And the perl pgm that develops counts from vm.stats.vm

SYSTEM MEMORY INFORMATION:
mem_wire:        1520701440 (   1450MB) [ 18%] Wired: disabled for paging out
mem_active:  +    957276160 (    912MB) [ 11%] Active: recently referenced
mem_inactive:+   3454586880 (   3294MB) [ 41%] Inactive: recently not referenced
mem_cache:   +            0 (      0MB) [  0%] Cached: almost avail. for allocation
mem_free:    +   1823854592 (   1739MB) [ 21%] Free: fully available for allocation
mem_gap_vm:  +    549380096 (    523MB) [  6%] Memory gap: UNKNOWN
-------------- ------------ ----------- ------
mem_all:     =   8305799168 (   7921MB) [100%] Total real memory managed
mem_gap_sys: +    240508928 (    229MB)        Memory gap: Kernel?!
-------------- ------------ -----------
mem_phys:    =   8546308096 (   8150MB)        Total real memory available
mem_gap_hw:  +     43626496 (     41MB)        Memory gap: Segment 
Mappings?!
-------------- ------------ -----------
mem_hw:      =   8589934592 (   8192MB)        Total real memory installed

SYSTEM MEMORY SUMMARY:
mem_used:        3311493120 (   3158MB) [ 38%] Logically used memory
mem_avail:   +   5278441472 (   5033MB) [ 61%] Logically available memory
-------------- ------------ ----------- ------
mem_total:   =   8589934592 (   8192MB) [100%] Logically total memory

The system I have the save a command on is older so an apache/php memory 
leak is not out of the question. The dipicted here is 11.3, apache24 and 
php7. I keep this one up by restarting one or more jails with swap space 
usage >50%. When it so it is almost instantaneous in both cases.