Re: help on memory usage ('top' and 'free' commands)

From: Jean-David Beyer (jdbeyer_at_exit109.com)
Date: 06/20/04 

Date: Sun, 20 Jun 2004 07:51:49 -0400

Juha Laiho wrote:
> Davide Bianchi <davideyeahsure@onlyforfun.net> said:
>
>>Anyway, if you are using SWAP, it means you don't have enough RAM.
>>Go to the shop and buy more ram.
>
>
> Why waste money for RAM just to keep inactuve data around? Many
> programs keep around some data they only use occasionally (or only
> once, as in startup).
>
> Swap is there to be used -- the real figure to monitor would be the
> paging activity (how many pages in/out per second). There consistent,
> excessive paging activity means that there is shortage of RAM. On
> Solaris, most references tend to say 200 pages (of 8kB) per second
> should be considered the limit -- I don't know what would be the
> comparable figure for Linux.

Here are three datapoints, based on the three machines I have running
Linux (Red Hat: 9 (256MByte RAM), 7.3 (512MByte RAM, and RHEL 3 ES
(4096MByte RAM), respectively):

touchl:jdbeyer[~]$ cat /proc/meminfo
         total: used: free: shared: buffers: cached:
Mem: 261914624 258203648 3710976 0 45121536 156897280
Swap: 536698880 27389952 509308928
MemTotal: 255776 kB
MemFree: 3624 kB
MemShared: 0 kB
Buffers: 44064 kB
Cached: 147784 kB
SwapCached: 5436 kB
Active: 170984 kB
ActiveAnon: 18484 kB
ActiveCache: 152500 kB
Inact_dirty: 8 kB
Inact_laundry: 34504 kB
Inact_clean: 4864 kB
Inact_target: 42072 kB
HighTotal: 0 kB
HighFree: 0 kB
LowTotal: 255776 kB
LowFree: 3624 kB
SwapTotal: 524120 kB
SwapFree: 497372 kB

valinuxl:jdbeyer[~]$ cat /proc/meminfo
         total: used: free: shared: buffers: cached:
Mem: 525983744 518803456 7180288 0 38703104 424636416
Swap: 1073733632 34594816 1039138816
MemTotal: 513656 kB
MemFree: 7012 kB
MemShared: 0 kB
Buffers: 37796 kB
Cached: 399704 kB
SwapCached: 14980 kB
Active: 330188 kB
ActiveAnon: 17608 kB
ActiveCache: 312580 kB
Inact_dirty: 0 kB
Inact_laundry: 112616 kB
Inact_clean: 11120 kB
Inact_target: 90784 kB
HighTotal: 0 kB
HighFree: 0 kB
LowTotal: 513656 kB
LowFree: 7012 kB
SwapTotal: 1048568 kB
SwapFree: 1014784 kB

         total: used: free: shared: buffers: cached:
Mem: 4224487424 4195180544 29306880 0 90345472 3693322240
Swap: 8389709824 2953216 8386756608
MemTotal: 4125476 kB
MemFree: 28620 kB
MemShared: 0 kB
Buffers: 88228 kB
Cached: 3604856 kB
SwapCached: 1904 kB
Active: 1222164 kB
ActiveAnon: 202204 kB
ActiveCache: 1019960 kB
Inact_dirty: 2033236 kB
Inact_laundry: 530012 kB
Inact_clean: 80340 kB
Inact_target: 773148 kB
HighTotal: 3276224 kB
HighFree: 12168 kB
LowTotal: 849252 kB
LowFree: 16452 kB
SwapTotal: 8193076 kB
SwapFree: 8190192 kB
HugePages_Total: 0
HugePages_Free: 0
Hugepagesize: 2048 kB

In all but the first machine, pageing rate is extremely low: a page or two
every few hours. For the first machine, it is a little higher, but less
than 2/second and still mostly less than that. The main things all these
machines are doing right now (when I made the measurements) is running
setiathome, which is CPU limited, but otherwise not very resource hungry.
The first machine is running one instance, the second one two instances,
and the third is running 2 instances at the moment but normally runs 4
(waiting for new work units). 

-- 
   .~.  Jean-David Beyer           Registered Linux User 85642.
   /V\                             Registered Machine   241939.
  /( )\ Shrewsbury, New Jersey     http://counter.li.org
  ^^-^^ 07:45:00 up 2 days, 7:09, 3 users, load average: 2.38, 2.23, 2.09

Relevant Pages

  • Re: excessive swap-in time
    ... Trying to do it all with RAM is just inefficient. ... I find that does not work well when the swapping is caused by excessive I/O ... Or you could have 5 TB of swap space. ...
    (comp.os.linux.development.system)
  • SLUB 0:1 SLAB (OOM during massive parallel kernel builds)
    ... 2G of RAM, 1G of swap partition. ... DMA per-cpu: ... kill process 25286 score 188662 or a child ...
    (Linux-Kernel)
  • Re: Swap space not used
    ... Swap is not "required". ... not sure - it was many, many, years ago, and thus, UNIX requires ... memory paging to work, and this is why UNIX has had such ... Now RAM is cheaper and so it's ...
    (Debian-User)
  • fork failed cannot allocate memory
    ... I have a Dell 2650, dual Xeon box, 2GB RAM, 6GB swap with PERC Hardware ... feeding the perl processes). ... Every week or two the box will stop allowing new netcool client ...
    (RedHat)
  • 2.6.26-rc5-mm2: OOM with 1G free swap
    ... OOM condition happened with 1G free swap. ... 4G RAM, 1G swap partition, normally LTP survives during much, much higher ... Call Trace: ... 675611 total pagecache pages ...
    (Linux-Kernel)