Xen project Mailing List

On Thu, Mar 22, 2018 at 10:44 PM, Christopher Myers <cmyers@xxxxxxxxxxxx> wrote:

A good command to try is "free":

cmyers@caradhras:~> free -h
              total        used        free      shared buff/cache   available
Mem:            15G        4.8G        6.2G        691M        4.2G         10G
Swap:          8.0G          0B        8.0G

In this case, you can see that my laptop is showing 6.2GB free out of 15GB. But, only 4.8GB is actually used by stuff; there's an extra 4.2GB used by the buffers and cache.

The longer a machine runs, the more will be used by that buff/cache line, until the amount of "free" dwindles down toward zero.

This is actually a good thing! It means that, instead of just sitting there unused, the computer is using ram to speed things up, instead of constantly having to go to disk for things that it frequently accesses.

A good explanation to read is here: https://serverfault.com/questions/85470/meaning-of-the-buffers-cache-line-in-the-output-of-free

Chris

From: Xen-users <xen-users-bounces@lists.xenproject.org> on behalf of Phil Susi <psusi@xxxxxxxxxx>
Sent: Thursday, March 22, 2018 8:01:01 AM
To: Minjun Hong; xen-users@xxxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] How could I find memory hogging process in Dom0?

On 3/22/2018 6:14 AM, Minjun Hong wrote:
> Hi.
> While installing and using Xen on my two PCs, I see that the dom0 is still
> running out of memory on one PC.

You are not running out of memory.

> I installed Xen in the same way (with same kernel version and same xen
> version) on the computers.
>
> But on one computer (labeled A), there is no problem, and on the other
> computer (labeled B), huge amounts of file page is consumed:
>
> # /proc/meminfo of A
>> MemTotal:        7545164 kB
>> MemFree:         6275968 kB
>> MemAvailable:    7039388 kB

7 gigs available.

>> Buffers:           43644 kB
>> *Cached:           937928 kB*
> # /proc/meminfo of B
>> MemTotal:        7487512 kB
>> MemFree:          138888 kB
>> MemAvailable:    6130396 kB

6.1 gigs available. Not much difference.

>> Buffers:          100832 kB
>> *Cached:          6227632 kB*

The only difference is that this one is using 6 gigs of the free memory
to cache files, since it has nothing better to do with it. This is
typical for a Linux system.

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Thanks for your answer, Christopher and Phil.

I also know that it is better to use the free memory as cache for file backed data or buffer rather than just leave it unused as you mentioned.

However, this is happening all the time, even if I reboot the machines.

And it causes performance degradation of B. So I need to find some way to resolve this problem.

After discovering performance degradation of B, I've reported some of the results of checking some of the two devices.

Because I installed Xen on the 2 PCs in the same way, I cannot understand why this is happening and I need to ask your help.