[systemd-devel] systemd-cgtop memory utilization display not useful

[Lennart Poettering]

On Fri, 14.11.14 20:36, Lutz Vieweg (lvml at 5t9.de) wrote:

> Hi,
> 
> I noticed that systemd-cgtop in the "memory" column
> displays (and uses for sorting) a value that does include
> the cache memory somehow attributed to the slice.

We use the "memory.usage_in_bytes" value as exposed by the memory
cgroup controller. I think the kernel cgroup maintainers are aware
that it is currently not ideal, and are revisiting what they export
there.

> 
> This makes little sense, as
> 
> a) cache memory is freed when a task requires that
>    memory for more important purposes, so cache memory
>    utilization never causes OOM-kills to happen
> 
> b) it causes usage numbers to be displayed that are
>    way beyond the memory.limit_in_bytes, because the
>    kernel (for good reason) does utilize more memory
>    for caching than what is limited by memory.limit_in_bytes
> 
> c) the sorting by "biggest memory user" is weird if
>    a slice is sorted first that might contain not a single
>    task, but which was associated with a recently running
>    task that read some 8 GB file, while another slice
>    containing a permanently running task that allocates
>    7 GB of RAM is sorted thereafter.
> 
> Please reconsider what values systemd-cgtop uses,
> "rss" and "rss-huge" from "memory.stat" might be better
> candidates than the currently used.

Last time I talked about this with Tejun he suggested sticking with
the current attribute, but that the kernel folks would change would it
would actually report to a more useful value.

Lennart

-- 
Lennart Poettering, Red Hat