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

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Date:   Fri, 28 Jan 2022 20:05:38 -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 10:35:22PM -0500, Waiman Long wrote:
> 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@...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?
> > > 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

My apologies.  My parsing of the ? statements was off.  FWIW putting

	', name'

on the next line would make it more clear...  But I see now...

Sorry,
Ira

> 
> Cheers,
> Longman
>