Gaps in memory usage summary!?

[Bernd Walter]

On Fri, Sep 19, 2003 at 11:11:39PM +0200, Ralf S. Engelschall wrote:
> ------------------------------------------------------------------------------
> FreeBSD-5.1-CURRENT/alpha
> 
> SYSTEM MEMORY INFORMATION:
> mem_wire:          32555008 (     31MB) [ 12%] Wired: disabled for paging out
> mem_active:  +     57344000 (     54MB) [ 22%] Active: recently referenced
> mem_inactive:+    116170752 (    110MB) [ 45%] Inactive: recently not referenced
> mem_cache:   +      4620288 (      4MB) [  1%] Cached: almost avail. for allocation
> mem_free:    +     12484608 (     11MB) [  4%] Free: fully available for allocation
> mem_gap_vm:  +     31113216 (     29MB) [ 12%] Memory gap: UNKNOWN
> -------------- ------------ ----------- ------
> mem_all:     =    254287872 (    242MB) [100%] Total real memory managed
> mem_gap_sys: +     11116544 (     10MB)        Memory gap: Kernel?!
> -------------- ------------ -----------
> mem_phys:    =    265404416 (    253MB)        Total real memory available
> mem_gap_hw:  +      3031040 (      2MB)        Memory gap: Segment Mappings?!
> -------------- ------------ -----------
> mem_hw:      =    268435456 (    256MB)        Total real memory installed
> 
> SYSTEM MEMORY SUMMARY:
> mem_used:         121012224 (    115MB) [ 47%] Logically unused memory
> mem_avail:   +    133275648 (    127MB) [ 52%] Logically available memory
> -------------- ------------ ----------- ------
> mem_total:   =    254287872 (    242MB) [100%] Logically total memory
> ------------------------------------------------------------------------------
> 
> My remaining questions now are:
> 
> 1. What memory is "map_gap_vm" and why is there no such gap on Intel
>    boxes but on Alpha boxes? The number I arithmetically calculate is
> 
>    vm.stats.vm.v_page_count
>    - (  vm.stats.vm.v_wire_count
>       + vm.stats.vm.v_active_count
>       + vm.stats.vm.v_inactive_count
>       + vm.stats.vm.v_cache_count
>       + vm.stats.vm.v_free_count )
> 
>    and I always would expect 0 here, but as you can see it is not at
>    least on Alpha. Is this a bug in our VM statistic code? Any clues?

This point is interesting.
On two current alphas I see large positive values:
mem_gap_vm:  +     30744576 (     29MB) [ 12%] Memory gap: UNKNOWN
mem_gap_vm:  +     98672640 (     94MB) [  4%] Memory gap: UNKNOWN

On a stable system I get the following:
[296]srv1.cosmo-project.de# perl ~/freebsd-memory 
SYSTEM MEMORY INFORMATION:
mem_wire:          47742976 (     45MB) [ 38%] Wired: disabled for paging out
mem_active:  +     58908672 (     56MB) [ 47%] Active: recently referenced
mem_inactive:+     11059200 (     10MB) [  8%] Inactive: recently not referenced
mem_cache:   +      6635520 (      6MB) [  5%] Cached: almost avail. for allocation
mem_free:    +       696320 (      0MB) [  0%] Free: fully available for allocation
mem_gap_vm:  +       -16384 (      0MB) [  0%] Memory gap: UNKNOWN
-------------- ------------ ----------- ------
mem_all:     =    125026304 (    119MB) [100%] Total real memory managed
mem_gap_sys: +      6660096 (      6MB)        Memory gap: Kernel?!
-------------- ------------ -----------
mem_phys:    =    131686400 (    125MB)        Total real memory available
mem_gap_hw:  +      2531328 (      2MB)        Memory gap: Segment Mappings?!
-------------- ------------ -----------
mem_hw:      =    134217728 (    128MB)        Total real memory installed

SYSTEM MEMORY SUMMARY:
mem_used:         106635264 (    101MB) [ 85%] Logically unused memory
mem_avail:   +     18391040 (     17MB) [ 14%] Logically available memory
-------------- ------------ ----------- ------
mem_total:   =    125026304 (    119MB) [100%] Logically total memory

[298]srv1.cosmo-project.de# perl ~/freebsd-memory
SYSTEM MEMORY INFORMATION:
mem_wire:          49479680 (     47MB) [ 39%] Wired: disabled for paging out
mem_active:  +     55934976 (     53MB) [ 44%] Active: recently referenced
mem_inactive:+     10821632 (     10MB) [  8%] Inactive: recently not referenced
mem_cache:   +      8085504 (      7MB) [  6%] Cached: almost avail. for allocation
mem_free:    +       696320 (      0MB) [  0%] Free: fully available for allocation
mem_gap_vm:  +         8192 (      0MB) [  0%] Memory gap: UNKNOWN
-------------- ------------ ----------- ------
mem_all:     =    125026304 (    119MB) [100%] Total real memory managed
mem_gap_sys: +      6660096 (      6MB)        Memory gap: Kernel?!
-------------- ------------ -----------
mem_phys:    =    131686400 (    125MB)        Total real memory available
mem_gap_hw:  +      2531328 (      2MB)        Memory gap: Segment Mappings?!
-------------- ------------ -----------
mem_hw:      =    134217728 (    128MB)        Total real memory installed

SYSTEM MEMORY SUMMARY:
mem_used:         105422848 (    100MB) [ 84%] Logically unused memory
mem_avail:   +     19603456 (     18MB) [ 15%] Logically available memory
-------------- ------------ ----------- ------
mem_total:   =    125026304 (    119MB) [100%] Logically total memory

Maybe a timing glitch on those values for -stable and a leak on
-current?
However - I'm not shure that memory always have to be on those lists.

> 2. What memory is "mem_gap_sys", i.e.
>    (hw.physmem - (vm.stats.vm.v_page_count * hw.pagesize)) ?
>    Is this the loaded kernel code?

I'm not shure, but I asume that's the kernel and static startup
allocation.

> 3. What memory is "mem_gap_hw", i.e.
>    (rounded(hw.physmem) - hw.physmem) ?
>    Is this caused by some special hardware memory segmenting?

On alpha systems this is typically PAL/SRM memory which is not
available to the OS.
On x86 systems sometimes ROM shadow and so on is not available.

-- 
B.Walter                   BWCT                http://www.bwct.de
ticso at bwct.de                                  info at bwct.de