linux-kernel - Re: [PATCH] memcg-v1: Enable setting memory min, low, high

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Message-ID: <2023040529-commodore-humongous-47c3@gregkh>
Date:   Wed, 5 Apr 2023 13:23:02 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Shaun Tancheff <shaun.tancheff@...il.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Shaun Tancheff <shaun.tancheff@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] memcg-v1: Enable setting memory min, low, high

On Wed, Apr 05, 2023 at 06:01:07PM +0700, Shaun Tancheff wrote:
> From: Shaun Tancheff <shaun.tancheff@....com>
> 
> For users that are unable to update to memcg-v2 this
> provides a method where memcg-v1 can more effectively
> apply enough memory pressure to effectively throttle
> filesystem I/O or otherwise minimize being memcg oom
> killed at the expense of reduced performance.
> 
> This patch extends the memcg-v1 legacy sysfs entries
> with:
>     limit_in_bytes.min, limit_in_bytes.low and
>     limit_in_bytes.high
> Since old software will need to be updated to take
> advantage of the new files a secondary method
> of setting min, low and high based on a percentage
> of the limit is also provided. The percentages
> are determined by module parameters.
> 
> The available module parameters can be set at
> kernel boot time, for example:
>    memcontrol.memcg_min=10
>    memcontrol.memcg_low=30
>    memcontrol.memcg_high=80
> 
> Would set min to 10%, low to 30% and high to 80% of
> the value written to:
>   /sys/fs/cgroup/memory/<grp>/memory.limit_in_bytes
> 
> Signed-off-by: Shaun Tancheff <shaun.tancheff@....com>
> ---
> v0: Initial hard coded limits by percent.
> v1: Added sysfs access and module parameters for percent values to enable
> v2: Fix 32-bit, remove need for missing __udivdi3
>  mm/memcontrol.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 82 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 2eee092f8f11..3cf8386f4f45 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -73,6 +73,18 @@
>  
>  #include <trace/events/vmscan.h>
>  
> +static unsigned int memcg_v1_min_default_percent;
> +module_param_named(memcg_min, memcg_v1_min_default_percent, uint, 0600);
> +MODULE_PARM_DESC(memcg_min, "memcg v1 min default percent");
> +
> +static unsigned int memcg_v1_low_default_percent;
> +module_param_named(memcg_low, memcg_v1_low_default_percent, uint, 0600);
> +MODULE_PARM_DESC(memcg_low, "memcg v1 low default percent");
> +
> +static unsigned int memcg_v1_high_default_percent;
> +module_param_named(memcg_high, memcg_v1_high_default_percent, uint, 0600);
> +MODULE_PARM_DESC(memcg_high, "memcg v1 high default percent");

This is not the 1990's, why are you using module parameters for this?
And this isn't a module, so why use module options, how are you supposed
to set them?

And you didn't document them anywhere?

Also, why is this cc: stable?

thanks,

greg k-h