Re: [PATCH v2 -next] cgroup/misc: Introduce misc.peak

[xiujianfeng <xiujianfeng@huawei.com>]

On 2024/7/2 8:41, Xiu Jianfeng wrote:
> Introduce misc.peak to record the historical maximum usage of the
> resource, as in some scenarios the value of misc.max could be
> adjusted based on the peak usage of the resource.
> 
> Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
> 
> ---
> v2: use cmpxchg to update the watermark
> ---
>  Documentation/admin-guide/cgroup-v2.rst |  9 ++++++
>  include/linux/misc_cgroup.h             |  2 ++
>  kernel/cgroup/misc.c                    | 39 +++++++++++++++++++++++++
>  3 files changed, 50 insertions(+)
> 
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index ae0fdb6fc618..468a95379009 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -2646,6 +2646,15 @@ Miscellaneous controller provides 3 interface files. If two misc resources (res_
>  	  res_a 3
>  	  res_b 0
>  
> +  misc.peak
> +        A read-only flat-keyed file shown in all cgroups.  It shows the
> +        historical maximum usage of the resources in the cgroup and its
> +        children.::
> +
> +	  $ cat misc.peak
> +	  res_a 10
> +	  res_b 8
> +
>    misc.max
>          A read-write flat-keyed file shown in the non root cgroups. Allowed
>          maximum usage of the resources in the cgroup and its children.::
> diff --git a/include/linux/misc_cgroup.h b/include/linux/misc_cgroup.h
> index e799b1f8d05b..faf72a537596 100644
> --- a/include/linux/misc_cgroup.h
> +++ b/include/linux/misc_cgroup.h
> @@ -30,11 +30,13 @@ struct misc_cg;
>  /**
>   * struct misc_res: Per cgroup per misc type resource
>   * @max: Maximum limit on the resource.
> + * @watermark: Historical maximum usage of the resource.
>   * @usage: Current usage of the resource.
>   * @events: Number of times, the resource limit exceeded.
>   */
>  struct misc_res {
>  	u64 max;
> +	u64 watermark;
>  	atomic64_t usage;
>  	atomic64_t events;
>  };
> diff --git a/kernel/cgroup/misc.c b/kernel/cgroup/misc.c
> index 79a3717a5803..42642a96f4dc 100644
> --- a/kernel/cgroup/misc.c
> +++ b/kernel/cgroup/misc.c
> @@ -121,6 +121,17 @@ static void misc_cg_cancel_charge(enum misc_res_type type, struct misc_cg *cg,
>  		  misc_res_name[type]);
>  }
>  
> +static void misc_cg_update_watermark(struct misc_res *res, u64 new_usage)
> +{
> +	u64 old;
> +
> +	do {
> +		old = READ_ONCE(res->watermark);
> +		if (cmpxchg(&res->watermark, old, new_usage) == old)
> +			break;
> +	} while (0);

oops! should be while (1) here.


> +}
> +
>  /**
>   * misc_cg_try_charge() - Try charging the misc cgroup.
>   * @type: Misc res type to charge.
> @@ -159,6 +170,7 @@ int misc_cg_try_charge(enum misc_res_type type, struct misc_cg *cg, u64 amount)
>  			ret = -EBUSY;
>  			goto err_charge;
>  		}
> +		misc_cg_update_watermark(res, new_usage);
>  	}
>  	return 0;
>  
> @@ -307,6 +319,29 @@ static int misc_cg_current_show(struct seq_file *sf, void *v)
>  	return 0;
>  }
>  
> +/**
> + * misc_cg_peak_show() - Show the peak usage of the misc cgroup.
> + * @sf: Interface file
> + * @v: Arguments passed
> + *
> + * Context: Any context.
> + * Return: 0 to denote successful print.
> + */
> +static int misc_cg_peak_show(struct seq_file *sf, void *v)
> +{
> +	int i;
> +	u64 watermark;
> +	struct misc_cg *cg = css_misc(seq_css(sf));
> +
> +	for (i = 0; i < MISC_CG_RES_TYPES; i++) {
> +		watermark = READ_ONCE(cg->res[i].watermark);
> +		if (READ_ONCE(misc_res_capacity[i]) || watermark)
> +			seq_printf(sf, "%s %llu\n", misc_res_name[i], watermark);
> +	}
> +
> +	return 0;
> +}
> +
>  /**
>   * misc_cg_capacity_show() - Show the total capacity of misc res on the host.
>   * @sf: Interface file
> @@ -357,6 +392,10 @@ static struct cftype misc_cg_files[] = {
>  		.name = "current",
>  		.seq_show = misc_cg_current_show,
>  	},
> +	{
> +		.name = "peak",
> +		.seq_show = misc_cg_peak_show,
> +	},
>  	{
>  		.name = "capacity",
>  		.seq_show = misc_cg_capacity_show,