Arch Linux

switch86

Member

Registered: 2008-08-25

Posts: 24

High amount of caching

Hello, all. First post about arch. Cool distro.

I'm pretty new to Arch but I've been using mainly Fedora for awhile now.  I've noticed something odd in Arch on my most recently acquired box.
Pentium 4 3.0ghz
2x 80GB HDD
1GB of memory
ATI Radeon AGP card
Arch 2008.6

I've noticed unusually high amounts of memory caching - unusual at least in my experience. The true usage is very low but I've been noticing the kernel caching about 800-900MB at any given time. The box is currently running without X as I try to troubleshoot my xorg.conf (that's an issue for another post). top, free -m, and /proc/meminfo routinely point to high amounts of memory being cached but actual usage has been hovering around 100MB at most.

$ free -m
             total       used       free     shared    buffers     cached
Mem:          1010        995         15          0         49        885
-/+ buffers/cache:         60        949
Swap:         1929          0       1929

$ cat /proc/meminfo
MemTotal:      1034704 kB
MemFree:         15400 kB
Buffers:         50436 kB
Cached:         906848 kB
SwapCached:          0 kB
Active:          40992 kB
Inactive:       921604 kB
HighTotal:      130512 kB
HighFree:          876 kB
LowTotal:       904192 kB
LowFree:         14524 kB
SwapTotal:     1975912 kB
SwapFree:      1975912 kB
[snipped]

$ top
top - 15:32:49 up 18:04,  1 user,  load average: 0.00, 0.00, 0.00
Tasks:  64 total,   1 running,  63 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.1%us,  0.2%sy,  0.0%ni, 99.3%id,  0.3%wa,  0.0%hi,  0.1%si,  0.0%st
Mem:   1034704k total,  1019416k used,    15288k free,    50536k buffers
Swap:  1975912k total,        0k used,  1975912k free,   906848k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
    1 root      20   0  1664  560  492 S    0  0.1   0:01.09 init
    2 root      15  -5     0    0    0 S    0  0.0   0:00.00 kthreadd
    3 root      RT  -5     0    0    0 S    0  0.0   0:00.01 migration/0
    4 root      15  -5     0    0    0 S    0  0.0   0:04.53 ksoftirqd/0
    5 root      RT  -5     0    0    0 S    0  0.0   0:00.00 watchdog/0
[snipped]

However, the machine is very responsive and is handling Samba service very quickly. I should mention I have one 1 GB swap per hard drive for a total of 2GB swap, but I've not even seen those swaps in use yet. Do I need to be concerned or is the high amount of caching something I should look into further? I know it's common for the kernel to cache some, but I've never seen the kernel cache ~95% of the system's available memory.

Thanks. Let me know if you need more output or further specs.

fwojciec

Member

Registered: 2007-05-20

Posts: 1,411

Re: High amount of caching

That's something to be happy about and shows how smart the kernel is.  Unused memory is wasted memory.  Would you rather have your system read everything from the HD over and over again?

switch86

Member

Registered: 2008-08-25

Posts: 24

Re: High amount of caching

Would you rather have your system read everything from the HD over and over again?

No, definitely not. I realize that caching is not the same as "using," but it seemed like a high amount of caching. I'm being paranoid, then?

lucke

Member

From: Poland

Registered: 2004-11-30

Posts: 4,018

Re: High amount of caching

If it really bothers you, you can add "sync; echo 3 >> /proc/sys/vm/drop_caches" to cron ;-)

Or you can just learn to enjoy better performance, ihih.

freakcode

Member

From: São Paulo - Brazil

Registered: 2007-11-03

Posts: 410

Website

Re: High amount of caching

Would you rather have your system read everything from the HD over and over again?

No, definitely not. I realize that caching is not the same as "using," but it seemed like a high amount of caching. I'm being paranoid, then?

Yes, you're. But the term is "ricer" I guess

Seriously now... you can argue what is a high amount of cache with kernel developers, they know better.

switch86

Member

Registered: 2008-08-25

Posts: 24

Re: High amount of caching

Okay, thanks guys. I'll shut up now.