linux-kernel - Re: [PATCH 2/2] mm/page_owner: Dump memcg information

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Date:   Fri, 28 Jan 2022 13:22:49 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Waiman Long <longman@...hat.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, Rafael Aquini <aquini@...hat.com>
Subject: Re: [PATCH 2/2] mm/page_owner: Dump memcg information

On Fri, Jan 28, 2022 at 02:56:42PM -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@...hat.com>
> ---
>  mm/page_owner.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index c52ce9d6bc3b..e5d8c642296b 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"
> @@ -339,6 +340,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  		depot_stack_handle_t handle)
>  {
>  	int ret = 0, pageblock_mt, page_mt;
> +	unsigned long __maybe_unused memcg_data;
>  	char *kbuf;
>  
>  	count = min_t(size_t, count, PAGE_SIZE);
> @@ -371,6 +373,32 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  			"Page has been migrated, last migrate reason: %s\n",
>  			migrate_reason_names[page_owner->last_migrate_reason]);
>  
> +#ifdef CONFIG_MEMCG
> +	/*
> +	 * 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)
> +			SNPRINTF(kbuf, count, ret, err, "Slab cache page\n");
> +
> +		if (!memcg)
> +			goto copy_out;
> +
> +		onlined = (memcg->css.flags & CSS_ONLINE);
> +		cgroup_name(memcg->css.cgroup, name, sizeof(name) - 1);
> +		SNPRINTF(kbuf, count, ret, err, "Charged %sto %smemcg %s\n",
                                                        ^^^
						Extra specifier?

Did this compile without warnings?

Ira

> +			PageMemcgKmem(page) ? "(via objcg) " : "",
> +			onlined ? "" : "offlined ", name);
> +	}
> +
> +copy_out:
> +#endif
> +
>  	SNPRINTF(kbuf, count, ret, err, "\n");
>  
>  	if (copy_to_user(buf, kbuf, ret))
> -- 
> 2.27.0
> 
>