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

[Waiman Long <longman@redhat.com>]

On 1/28/22 16:48, Ira Weiny wrote:
> On Fri, Jan 28, 2022 at 04:31:07PM -0500, Waiman Long wrote:
>> On 1/28/22 16:22, Ira Weiny wrote:
>>> 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@redhat.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?
>> Yes, there was no warning.
> But isn't that an extra specifier?

There are 3 arguments to the format string that match the 3 "%s" in it:

1) PageMemcgKmem(page) ? "(via objcg) " : ""
2) onlined ? "" : "offlined
3) name

Cheers,
Longman