Re: [PATCH] memcg: Add a new sysctl parameter for automatically setting memory.high

Waiman Long
2024-06-23T20:52:11Z

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@redhat.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);