[SOLVED] How available memory is showing up on Centos?

james000 · 10-05-2023, 09:45 AM

I am looking at my Centos VM and trying to understand memory. I know that cache + free memory is supposed to be available (for apps) memory. But here it is 431M + 2.1GB is free+cache. How 26gb is available ?

Code:

[root@Centos-4444 ~]# free -h
                total       used        free        shared      buff/cache      available
Mem:            31G         28G         431M        97M         2.1G            26G
Swap:           15G         19M         15G
[root@Centos-4444 ~]#

Problem is, monitoring tool is looking at free memory and creating ticket for us that free memory is only 431MB.
Please suggest. Thanks

computersavvy · 10-05-2023, 10:37 AM

The monitoring tool is only looking at one factor and does not understand how RAM is allocated nor how free is displaying the values.

There is probably a lot of stale data in the "used" space that could be cleared out (deleted or swapped out) when more space is needed thus a major portion of the "used" is actually "available". Systems are designed to keep data available for quick access as long as adequate RAM is there for the purpose, so unnecessary swapping or deletions are delayed.

The monitoring tool really should be looking at both "free" and "available".

Note mine here

Code:

# free -h
               total        used        free      shared  buff/cache   available
Mem:            31Gi        13Gi       1.9Gi       214Mi        16Gi        17Gi
Swap:          8.0Gi        17Mi       8.0Gi

I only have 32GB but used + available totals 40GB.
On yours used + available totals 54GB

The buff/cache value also factors into that.
Note that the used + free + shared + buff/cache ~= total, and available is a value that may be repurposed from all the others.

james000 · 10-05-2023, 10:54 AM

Quote:

Originally Posted by computersavvy

The monitoring tool is only looking at one factor and does not understand how RAM is allocated nor how free is displaying the values.

There is probably a lot of stale data in the "used" space that could be cleared out (deleted or swapped out) when more space is needed thus a major portion of the "used" is actually "available". Systems are designed to keep data available for quick access as long as adequate RAM is there for the purpose, so unnecessary swapping or deletions are delayed.

The monitoring tool really should be looking at both "free" and "available".

Note mine here

Code:

# free -h
               total        used        free      shared  buff/cache   available
Mem:            31Gi        13Gi       1.9Gi       214Mi        16Gi        17Gi
Swap:          8.0Gi        17Mi       8.0Gi

I only have 32GB but used + available totals 40GB.
On yours used + available totals 54GB

The buff/cache value also factors into that.
Note that the used + free + shared + buff/cache ~= total, and available is a value that may be repurposed from all the others.

In my case, should monitoring tool look at available+free (26gb + 431mb) as 26.5gb as 'true' free memory?
Only 5.5gb memory is in use then?

MadeInGermany · 10-05-2023, 02:09 PM

IMHO just "available" is the best bet.

lvm_ · 10-06-2023, 02:44 AM

Quote:

Originally Posted by james000

In my case, should monitoring tool look at available+free (26gb + 431mb) as 26.5gb as 'true' free memory?

No, just available. Why don't you read the man page?