linux-kernel - Re: [RFC] memcg: Add swappiness to cgroup2

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Message-ID: <20191225140546.GA311630@chrisdown.name>
Date:   Wed, 25 Dec 2019 14:05:46 +0000
From:   Chris Down <chris@...isdown.name>
To:     Hui Zhu <teawater@...il.com>
Cc:     hannes@...xchg.org, mhocko@...nel.org, vdavydov.dev@...il.com,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        Hui Zhu <teawaterz@...ux.alibaba.com>
Subject: Re: [RFC] memcg: Add swappiness to cgroup2

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@...ux.alibaba.com>
>---
> 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
>
>