[gllug] Memory Available

[Steve Nelson]

Hello Chaps,

Interesting memory usage question.  The following is output from a
production proxy server:

3:12:55  up 74 days, 19:21,  2 users,  load average: 0.00, 0.04, 0.09
94 processes: 93 sleeping, 1 running, 0 zombie, 0 stopped
CPU states:  cpu    user    nice  system    irq  softirq  iowait    idle
           total    0.0%    0.0%    0.3%   0.0%     0.0%    0.0%   99.6%
           cpu00    0.0%    0.0%    0.0%   0.0%     0.0%    0.0%  100.0%
           cpu01    0.2%    0.0%    0.4%   0.0%     0.0%    0.0%   99.4%
           cpu02    0.0%    0.0%    0.4%   0.0%     0.0%    0.2%   99.4%
           cpu03    0.0%    0.0%    0.4%   0.0%     0.0%    0.0%   99.6%
Mem:  2055472k av, 1908592k used,  146880k free,       0k shrd,  144056k buff
                   1395804k actv,  287124k in_d,   32712k in_c
Swap: 2097112k av,   13212k used, 2083900k free                 1616664k cached

# free
             total       used       free     shared    buffers     cached
Mem:       2055472    1908656     146816          0     144056    1616668
-/+ buffers/cache:     147932    1907540
Swap:      2097112      13212    2083900

# vmstat 5 5
procs                      memory      swap          io     system         cpu
 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy wa id
 0  0  13212 146816 144060 1616680    0    0     1     0    1     0  0  0  0  0
 0  0  13212 146816 144060 1616684    0    0     0    22  168    82  0  0  0 100
 0  0  13212 146816 144060 1616684    0    0     0    48  137    47  0  0  0 100
 0  0  13212 146816 144060 1616684    0    0     0     2  114    21  0  0  0 100
 0  0  13212 146816 144060 1616684    0    0     0    10  117    26  0  0  0 100

cat /proc/meminfo
        total:    used:    free:  shared: buffers:  cached:
Mem:  2104803328 1955205120 149598208        0 147517440 1662750720
Swap: 2147442688 13529088 2133913600
MemTotal:      2055472 kB
MemFree:        146092 kB
MemShared:           0 kB
Buffers:        144060 kB
Cached:        1616780 kB
SwapCached:       7000 kB
Active:        1395412 kB
ActiveAnon:      10980 kB
ActiveCache:   1384432 kB
Inact_dirty:    287240 kB
Inact_laundry:   54048 kB
Inact_clean:     32712 kB
Inact_target:   353880 kB
HighTotal:     1179596 kB
HighFree:       122672 kB
LowTotal:       875876 kB
LowFree:         23420 kB
SwapTotal:     2097112 kB
SwapFree:      2083900 kB
HugePages_Total:     0
HugePages_Free:      0
Hugepagesize:     2048 kB

There were a number of Java processes using a load of memory
(monitoring agents).  I killed the application to see if the memory
would reappear as available, but it is still cached, and so not
reported as available.

This behaviour is redolent of Solaris 7 (before the priority paging
patch) - in that cached pages were not made available to the page
reclaimation daemon.  In Solaris 8 and 9, cache is reported on the
freelist.  If I recall correctly there was an fs_flush function to
make this memory available on solaris 7.

How is this working under Linux?  Is this memory available? If so why
is it not reported as free?

# uname -a
Linux paul 2.4.21-20.ELsmp #1 SMP Wed Aug 18 20:46:40 EDT 2004 i686
i686 i386 GNU/Linux

Thanks,

Steve
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