Re: [RFC] memcg: Add swappiness to cgroup2

[Chris Down]

Hi Hui,

Hui Zhu writes:
> Even if cgroup2 has swap.max, swappiness is still a very useful config.
> This commit add swappiness to cgroup2.

When submitting patches like this, it's important to explain *why* you want it 
and what evidence there is. For example, how should one use this to compose a 
reasonable system? Why aren't existing protection controls sufficient for your 
use case? Where's the data?

Also, why would swappiness be something cgroup-specific instead of 
hardware-specific, when desired swappiness is really largely about the hardware 
you have in your system?

I struggle to think of situations where per-cgroup swappiness would be useful, 
since it's really not a workload-specific setting.

Thanks,

Chris

> Signed-off-by: Hui Zhu <teawaterz@xxxxxxxxxxxxxxxxx>
> ---
> mm/memcontrol.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index c5b5f74..e966396 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -7143,6 +7143,11 @@ static struct cftype swap_files[] = {
> 		.file_offset = offsetof(struct mem_cgroup, swap_events_file),
> 		.seq_show = swap_events_show,
> 	},
> +	{
> +		.name = "swappiness",
> +		.read_u64 = mem_cgroup_swappiness_read,
> +		.write_u64 = mem_cgroup_swappiness_write,
> +	},
> 	{ }	/* terminate */
> };
>
> --
> 2.7.4