memory usage of linux - aragorn/home GitHub Wiki

JK checked this in year 2012. But I assume, still most things are valid.

How to find out actual free or available memory of linux?

$ free; sync; echo 3 > /proc/sys/vm/drop_caches; free;
$ grep -E 'MemFree|Inactive' /proc/meminfo;

# example

root@sheldon:~# free; sync; echo 3 > /proc/sys/vm/drop_caches; free;
              total        used        free      shared  buff/cache   available
Mem:       16425092    10227228     4915028       42528     1282836     5732788
Swap:             0           0           0
              total        used        free      shared  buff/cache   available
Mem:       16425092    10227292     5938192       42528      259608     5835264
Swap:             0           0           0
root@sheldon:~# grep -E 'MemFree|Inactive' /proc/meminfo;
MemFree:         5936952 kB
Inactive:          62144 kB
Inactive(anon):    40692 kB
Inactive(file):    21452 kB
root@sheldon:~# 

Articles on linux memory

• http://stackoverflow.com/questions/658411/entries-in-proc-meminfo/6886706#6886706
• http://www.mjmwired.net/kernel/Documentation/filesystems/proc.txt

Generally,

MemTotal = MemFree + Active + Inactive + Slab + PageTables + VmallocUsed + X =~ MemFree + Active + Inactive + Slab + PageTables + VmallocUsed

Active + Inactive =~ Buffers + Cached + SwapCached + AnonPages

MemAvail : Amount of memory that user application can demand and get allocated in physical memory. =~ MemFree + Inactive

MemUsed by user and kernel = MemTotal - MemAvail = MemTotal - MemFree - Inactive =~ Active + Slab + PageTables + VmallocUsed

MemUsed by user =~ Active + VmallocUsed

MemUsed by kernel =~ Slab + PageTables