Re: [PATCH v2 3/3] mm/page_owner: Dump memcg information

[Mike Rapoport <rppt@kernel.org>]

On Sat, Jan 29, 2022 at 03:53:15PM -0500, Waiman Long wrote:
> It was found that a number of offlined memcgs were not freed because
> they were pinned by some charged pages that were present. Even "echo
> 1 > /proc/sys/vm/drop_caches" wasn't able to free those pages. These
> offlined but not freed memcgs tend to increase in number over time with
> the side effect that percpu memory consumption as shown in /proc/meminfo
> also increases over time.
> 
> In order to find out more information about those pages that pin
> offlined memcgs, the page_owner feature is extended to dump memory
> cgroup information especially whether the cgroup is offlined or not.
> 
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
>  mm/page_owner.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 28dac73e0542..8dc5cd0fa227 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -10,6 +10,7 @@
>  #include <linux/migrate.h>
>  #include <linux/stackdepot.h>
>  #include <linux/seq_file.h>
> +#include <linux/memcontrol.h>
>  #include <linux/sched/clock.h>
>  
>  #include "internal.h"
> @@ -331,6 +332,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  		depot_stack_handle_t handle)
>  {
>  	int ret, pageblock_mt, page_mt;
> +	unsigned long __maybe_unused memcg_data;
>  	char *kbuf;
>  
>  	count = min_t(size_t, count, PAGE_SIZE);
> @@ -365,6 +367,35 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  			migrate_reason_names[page_owner->last_migrate_reason]);
>  	}
>  
> +#ifdef CONFIG_MEMCG

Can we put all this along with the declaration of memcg_data in a helper
function please?

> +	/*
> +	 * Look for memcg information and print it out
> +	 */
> +	memcg_data = READ_ONCE(page->memcg_data);
> +	if (memcg_data) {
> +		struct mem_cgroup *memcg = page_memcg_check(page);
> +		bool onlined;
> +		char name[80];
> +
> +		if (memcg_data & MEMCG_DATA_OBJCGS)
> +			ret += scnprintf(kbuf + ret, count - ret,
> +					"Slab cache page\n");
> +
> +		if (!memcg)
> +			goto copy_out;
> +
> +		onlined = (memcg->css.flags & CSS_ONLINE);
> +		cgroup_name(memcg->css.cgroup, name, sizeof(name));
> +		ret += scnprintf(kbuf + ret, count - ret,
> +				"Charged %sto %smemcg %s\n",
> +				PageMemcgKmem(page) ? "(via objcg) " : "",
> +				onlined ? "" : "offlined ",
> +				name);
> +	}
> +
> +copy_out:
> +#endif
> +
>  	ret += snprintf(kbuf + ret, count - ret, "\n");
>  	if (ret >= count)
>  		goto err;
> -- 
> 2.27.0
> 
> 

-- 
Sincerely yours,
Mike.