About swapaccount=

About swapaccount=

[Jonas Schäfer]

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Hi there,

By coincidence, I found this log message in my kernel logs:

Mär 02 17:23:19 sinistra kernel: The swapaccount= commandline option is 
deprecated. Please report your usecase to linux-mm@kvack.org if you depend on 
this functionality.

My usecase does depend on this in the following way:

I use LXC extensively to isolate workloads from one another. Kind of like 
docker, but with full operating systems inside.

Before I found out about swapaccount, I often ran into the issue that one 
misbehaving workload from one of those containers would bring the entire 
machine to a halt because it occupied lots of swap, and thus triggered 
significant slowdown.

With swapaccount, I limit swap to about 10% of the RAM assigned to the 
containers. This allows them to swap out unused stuff, but invokes the OOM 
killer before any significant slowdown happens.

The alternative would be to turn off swap for the system entirely, but it is 
running fairly efficiently thanks to swapping stuff out.

I'd be interested to hear about alternatives.

Thanks for hearing me, anyway.

kind regards,
Jonas Schäfer

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Re: About swapaccount=

[Yosry Ahmed]

On Thu, Mar 2, 2023 at 11:01 AM Jonas Schäfer <jonas@wielicki.name> wrote:
>
> Hi there,
>
> By coincidence, I found this log message in my kernel logs:
>
> Mär 02 17:23:19 sinistra kernel: The swapaccount= commandline option is
> deprecated. Please report your usecase to linux-mm@kvack.org if you depend on
> this functionality.
>
> My usecase does depend on this in the following way:
>
> I use LXC extensively to isolate workloads from one another. Kind of like
> docker, but with full operating systems inside.
>
> Before I found out about swapaccount, I often ran into the issue that one
> misbehaving workload from one of those containers would bring the entire
> machine to a halt because it occupied lots of swap, and thus triggered
> significant slowdown.
>
> With swapaccount, I limit swap to about 10% of the RAM assigned to the
> containers. This allows them to swap out unused stuff, but invokes the OOM
> killer before any significant slowdown happens.
>
> The alternative would be to turn off swap for the system entirely, but it is
> running fairly efficiently thanks to swapping stuff out.
>
> I'd be interested to hear about alternatives.
>
> Thanks for hearing me, anyway.

If I understand correctly you were setting swapaccount=1, right?

IIRC, swapaccount= was deprecated in the sense that it is always on
now (i.e you cannot set swapaccount=0).

>
> kind regards,
> Jonas Schäfer

Re: About swapaccount=

[Jonas Schäfer]

Hi Yosry,

On Donnerstag, 2. März 2023 20:12:43 CET Yosry Ahmed wrote:
> On Thu, Mar 2, 2023 at 11:01 AM Jonas Schäfer <jonas@wielicki.name> wrote:
> > Hi there,
> > 
> > By coincidence, I found this log message in my kernel logs:
> > 
> > Mär 02 17:23:19 sinistra kernel: The swapaccount= commandline option is
> > deprecated. Please report your usecase to linux-mm@kvack.org if you depend
> > on this functionality.
> > 
> > My usecase does depend on this in the following way:
> > 
> > I use LXC extensively to isolate workloads from one another. Kind of like
> > docker, but with full operating systems inside.
> > 
> > Before I found out about swapaccount, I often ran into the issue that one
> > misbehaving workload from one of those containers would bring the entire
> > machine to a halt because it occupied lots of swap, and thus triggered
> > significant slowdown.
> > 
> > With swapaccount, I limit swap to about 10% of the RAM assigned to the
> > containers. This allows them to swap out unused stuff, but invokes the OOM
> > killer before any significant slowdown happens.
> > 
> > The alternative would be to turn off swap for the system entirely, but it
> > is running fairly efficiently thanks to swapping stuff out.
> > 
> > I'd be interested to hear about alternatives.
> > 
> > Thanks for hearing me, anyway.
> 
> If I understand correctly you were setting swapaccount=1, right?
> 
> IIRC, swapaccount= was deprecated in the sense that it is always on
> now (i.e you cannot set swapaccount=0).

Thank you for the swift reply. Indeed, I am using swapaccount=1, so I assumed 
the deprecation warning was related to =1. If =1 continues to work as default, 
that just means I have one less thing to carry around in the grub config and 
is not a problem at all!

Thanks!

kind regards,
Jonas