Re: [PATCH] Port hierarchical_mem{ory,sw}_limit cgroup1->cgroup2

[Waiman Long <longman@redhat.com>]

On 2/9/24 09:48, Jan Kratochvil (Azul) wrote:
> Hello,
>
> cgroup1 (by function memcg1_stat_format) already contains two lines
> 	hierarchical_memory_limit %llu
> 	hierarchical_memsw_limit %llu
>
> which are useful for userland to easily and performance-wise find out the
> effective cgroup limits being applied. Otherwise userland has to
> open+read+close the file "memory.max" and/or "memory.swap.max" in multiple
> parent directories of a nested cgroup.
>
> For cgroup1 it was implemented by:
> 	memcg: show real limit under hierarchy mode
> 	https://github.com/torvalds/linux/commit/fee7b548e6f2bd4bfd03a1a45d3afd593de7d5e9
> 	Date:   Wed Jan 7 18:08:26 2009 -0800
>
> But for cgroup2 it has been missing so far, this is just a copy-paste of the
> cgroup1 code. I have added it to the end of "memory.stat" to prevent possible
> compatibility problems with existing code parsing that file.
>
>
> Jan Kratochvil
>
>
> Signed-off-by: Jan Kratochvil (Azul) <jkratochvil@azul.com>
>
>   mm/memcontrol.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 46d8d0211..39f2a4a06 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1636,6 +1636,8 @@ static inline unsigned long memcg_page_state_local_output(
>   static void memcg_stat_format(struct mem_cgroup *memcg, struct seq_buf *s)
>   {
>   	int i;
> +	unsigned long memory, memsw;
> +	struct mem_cgroup *mi;
>   
>   	/*
>   	 * Provide statistics on the state of the memory subsystem as
> @@ -1682,6 +1684,17 @@ static void memcg_stat_format(struct mem_cgroup *memcg, struct seq_buf *s)
>   			       memcg_events(memcg, memcg_vm_event_stat[i]));
>   	}
>   
> +	/* Hierarchical information */
> +	memory = memsw = PAGE_COUNTER_MAX;
> +	for (mi = memcg; mi; mi = parent_mem_cgroup(mi)) {
> +		memory = min(memory, READ_ONCE(mi->memory.max));
> +		memsw = min(memsw, READ_ONCE(mi->memsw.max));
> +	}
> +	seq_buf_printf(s, "hierarchical_memory_limit %llu\n",
> +		       (u64)memory * PAGE_SIZE);
> +	seq_buf_printf(s, "hierarchical_memsw_limit %llu\n",
> +		       (u64)memsw * PAGE_SIZE);
> +
>   	/* The above should easily fit into one page */
>   	WARN_ON_ONCE(seq_buf_has_overflowed(s));
>   }

I don't think we use mi->memsw in cgroup v2, only memory and swap should 
be used.

Cheers,
Longman

>