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Message-ID: <77d4299e-e1ee-4471-9b53-90957daa984d@redhat.com>
Date: Sun, 23 Jun 2024 16:52:00 -0400
From: Waiman Long <longman@...hat.com>
To: Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Muchun Song <muchun.song@...ux.dev>,
 Andrew Morton <akpm@...ux-foundation.org>, Jonathan Corbet <corbet@....net>,
 Shakeel Butt <shakeel.butt@...ux.dev>
Cc: linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
 linux-mm@...ck.org, Alex Kalenyuk <akalenyu@...hat.com>,
 Peter Hunt <pehunt@...hat.com>, linux-doc@...r.kernel.org
Subject: Re: [PATCH] memcg: Add a new sysctl parameter for automatically
 setting memory.high

Correct some email addresses.

On 6/23/24 16:45, Waiman Long wrote:
> With memory cgroup v1, there is only a single "memory.limit_in_bytes"
> to be set to specify the maximum amount of memory that is allowed to
> be used. So a lot of memory cgroup using tools and applications allow
> users to specify a single memory limit. When they migrate to cgroup
> v2, they use the given memory limit to set memory.max and disregard
> memory.high for the time being.
>
> Without properly setting memory.high, these user space applications
> cannot make use of the memory cgroup v2 ability to further reduce the
> chance of OOM kills by throttling and early memory reclaim.
>
> This patch adds a new sysctl parameter "vm/memory_high_autoset_ratio"
> to enable setting "memory.high" automatically whenever "memory.max" is
> set as long as "memory.high" hasn't been explicitly set before. This
> will allow a system administrator or a middleware layer to greatly
> reduce the chance of memory cgroup OOM kills without worrying about
> how to properly set memory.high.
>
> The new sysctl parameter will allow a range of 0-100. The default value
> of 0 will disable memory.high auto setting. For any non-zero value "n",
> the actual ratio used will be "n/(n+1)". A user cannot set a fraction
> less than 1/2.
>
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>   Documentation/admin-guide/sysctl/vm.rst | 10 ++++++
>   include/linux/memcontrol.h              |  3 ++
>   mm/memcontrol.c                         | 41 +++++++++++++++++++++++++
>   3 files changed, 54 insertions(+)
>
> diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
> index e86c968a7a0e..250ec39dd5af 100644
> --- a/Documentation/admin-guide/sysctl/vm.rst
> +++ b/Documentation/admin-guide/sysctl/vm.rst
> @@ -46,6 +46,7 @@ Currently, these files are in /proc/sys/vm:
>   - mem_profiling         (only if CONFIG_MEM_ALLOC_PROFILING=y)
>   - memory_failure_early_kill
>   - memory_failure_recovery
> +- memory_high_autoset_ratio
>   - min_free_kbytes
>   - min_slab_ratio
>   - min_unmapped_ratio
> @@ -479,6 +480,15 @@ Enable memory failure recovery (when supported by the platform)
>   0: Always panic on a memory failure.
>   
>   
> +memory_high_autoset_ratio
> +=========================
> +
> +Specify a ratio by which memory.high should be set as a fraction of
> +memory.max if it hasn't been explicitly set before.  It allows a range
> +of 0-100.  The default value of 0 means auto setting will be disabled.
> +For any non-zero value "n", the actual ratio used will be "n/(n+1)".
> +
> +
>   min_free_kbytes
>   ===============
>   
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 030d34e9d117..6be161a6b922 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -221,6 +221,9 @@ struct mem_cgroup {
>   	 */
>   	bool oom_group;
>   
> +	/* %true if memory.high has been explicitly set */
> +	bool memory_high_set;
> +
>   	/* protected by memcg_oom_lock */
>   	bool		oom_lock;
>   	int		under_oom;
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 71fe2a95b8bd..2cfb000bf543 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -48,6 +48,7 @@
>   #include <linux/swap.h>
>   #include <linux/swapops.h>
>   #include <linux/spinlock.h>
> +#include <linux/sysctl.h>
>   #include <linux/eventfd.h>
>   #include <linux/poll.h>
>   #include <linux/sort.h>
> @@ -6889,6 +6890,35 @@ static void mem_cgroup_attach(struct cgroup_taskset *tset)
>   }
>   #endif
>   
> +/*
> + * The memory.high autoset ratio specifies a ratio by which memory.high
> + * should be set as a fraction of memory.max if it hasn't been explicitly
> + * set before. The default value of 0 means auto setting will be disabled.
> + * For any non-zero value "n", the actual ratio is "n/(n+1)".
> + */
> +static int sysctl_memory_high_autoset_ratio;
> +
> +#ifdef CONFIG_SYSCTL
> +static struct ctl_table memcg_table[] = {
> +	{
> +		.procname	= "memory_high_autoset_ratio",
> +		.data		= &sysctl_memory_high_autoset_ratio,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= SYSCTL_ZERO,
> +		.extra2		= SYSCTL_ONE_HUNDRED,
> +	},
> +};
> +
> +static inline void memcg_sysctl_init(void)
> +{
> +	register_sysctl_init("vm", memcg_table);
> +}
> +#else
> +static void memcg_sysctl_init(void)	{ }
> +#endif /* CONFIG_SYSCTL */
> +
>   static int seq_puts_memcg_tunable(struct seq_file *m, unsigned long value)
>   {
>   	if (value == PAGE_COUNTER_MAX)
> @@ -6982,6 +7012,7 @@ static ssize_t memory_high_write(struct kernfs_open_file *of,
>   		return err;
>   
>   	page_counter_set_high(&memcg->memory, high);
> +	memcg->memory_high_set = true;
>   
>   	for (;;) {
>   		unsigned long nr_pages = page_counter_read(&memcg->memory);
> @@ -7023,6 +7054,7 @@ static ssize_t memory_max_write(struct kernfs_open_file *of,
>   	unsigned int nr_reclaims = MAX_RECLAIM_RETRIES;
>   	bool drained = false;
>   	unsigned long max;
> +	unsigned int high_ratio = sysctl_memory_high_autoset_ratio;
>   	int err;
>   
>   	buf = strstrip(buf);
> @@ -7032,6 +7064,13 @@ static ssize_t memory_max_write(struct kernfs_open_file *of,
>   
>   	xchg(&memcg->memory.max, max);
>   
> +	if (high_ratio && !memcg->memory_high_set) {
> +		/* Set memory.high as a fraction of memory.max */
> +		unsigned long high = max * high_ratio / (high_ratio + 1);
> +
> +		page_counter_set_high(&memcg->memory, high);
> +	}
> +
>   	for (;;) {
>   		unsigned long nr_pages = page_counter_read(&memcg->memory);
>   
> @@ -7977,6 +8016,8 @@ static int __init mem_cgroup_init(void)
>   		soft_limit_tree.rb_tree_per_node[node] = rtpn;
>   	}
>   
> +	memcg_sysctl_init();
> +
>   	return 0;
>   }
>   subsys_initcall(mem_cgroup_init);


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