Re: [PATCH v4 3/4] mm/page_owner: Print memcg information

[Mike Rapoport <rppt@kernel.org>]

On Wed, Feb 02, 2022 at 03:30:35PM -0500, Waiman Long wrote:
> It was found that a number of offline 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 offline
> 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
> offline memcgs, the page_owner feature is extended to print memory
> cgroup information especially whether the cgroup is offline or not.
> RCU read lock is taken when memcg is being accessed to make sure
> that it won't be freed.
> 
> Signed-off-by: Waiman Long <longman@redhat.com>
> Acked-by: David Rientjes <rientjes@google.com>
> Acked-by: Roman Gushchin <guro@fb.com>

Acked-by: Mike Rapoport <rppt@linux.ibm.com>

And my akcs for the first two patches are missing somehow in v4...

> ---
>  mm/page_owner.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
> 
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 28dac73e0542..f7820357e4d4 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"
> @@ -325,6 +326,45 @@ void pagetypeinfo_showmixedcount_print(struct seq_file *m,
>  	seq_putc(m, '\n');
>  }
>  
> +/*
> + * Looking for memcg information and print it out
> + */
> +static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret,
> +					 struct page *page)
> +{
> +#ifdef CONFIG_MEMCG
> +	unsigned long memcg_data;
> +	struct mem_cgroup *memcg;
> +	bool online;
> +	char name[80];
> +
> +	rcu_read_lock();
> +	memcg_data = READ_ONCE(page->memcg_data);
> +	if (!memcg_data)
> +		goto out_unlock;
> +
> +	if (memcg_data & MEMCG_DATA_OBJCGS)
> +		ret += scnprintf(kbuf + ret, count - ret,
> +				"Slab cache page\n");
> +
> +	memcg = page_memcg_check(page);
> +	if (!memcg)
> +		goto out_unlock;
> +
> +	online = (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) " : "",
> +			online ? "" : "offline ",
> +			name);
> +out_unlock:
> +	rcu_read_unlock();
> +#endif /* CONFIG_MEMCG */
> +
> +	return ret;
> +}
> +
>  static ssize_t
>  print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  		struct page *page, struct page_owner *page_owner,
> @@ -365,6 +405,8 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  			migrate_reason_names[page_owner->last_migrate_reason]);
>  	}
>  
> +	ret = print_page_owner_memcg(kbuf, count, ret, page);
> +
>  	ret += snprintf(kbuf + ret, count - ret, "\n");
>  	if (ret >= count)
>  		goto err;
> -- 
> 2.27.0
> 
> 

-- 
Sincerely yours,
Mike.