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Message-ID: <870aa2af-62b7-48ba-b1a0-77b651352211@nebius.com>
Date: Wed, 13 Sep 2023 12:35:15 +0200
From: Dmitry Yakunin <zeil@...ius.com>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
NB-Core Team <NB-CoreTeam@...ius.com>,
"tj@...nel.org" <tj@...nel.org>,
"hannes@...xchg.org" <hannes@...xchg.org>,
"mhocko@...nel.org" <mhocko@...nel.org>,
Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
Andrey Ryabinin <arbn@...dex-team.com>
Subject: Re: [RFC PATCH 1/3] cgroup: list all subsystem states in debugfs
files
Sure, if you can share you work it would be nice. Thank you.
On 12.09.2023 00:16, Yosry Ahmed wrote:
> On Mon, Sep 11, 2023 at 12:55 AM Yakunin, Dmitry (Nebius)
> <zeil@...ius.com> wrote:
>> After removing cgroup subsystem state could leak or live in background
>> forever because it is pinned by some reference. For example memory cgroup
>> could be pinned by pages in cache or tmpfs.
>>
>> This patch adds common debugfs interface for listing basic state for each
>> controller. Controller could define callback for dumping own attributes.
>>
>> In file /sys/kernel/debug/cgroup/<controller> each line shows state in
>> format: <common_attr>=<value>... [-- <controller_attr>=<value>... ]
>>
>> Common attributes:
>>
>> css - css pointer
>> cgroup - cgroup pointer
>> id - css id
>> ino - cgroup inode
>> flags - css flags
>> refcnt - css atomic refcount, for online shows huge bias
>> path - cgroup path
>>
>> This patch adds memcg attributes:
>>
>> mem_id - 16-bit memory cgroup id
>> memory - charged pages
>> memsw - charged memory+swap for v1 and swap for v2
>> kmem - charged kernel pages
>> tcpmem - charged tcp pages
>> shmem - shmem/tmpfs pages
>>
>> Link: https://lore.kernel.org/lkml/153414348591.737150.14229960913953276515.stgit@buzz
>> Suggested-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
>> Reviewed-by: Andrey Ryabinin <arbn@...dex-team.com>
>> Signed-off-by: Dmitry Yakunin <zeil@...ius.com>
> FWIW, I was just recently working on a debugfs directly that exposes a
> list of all zombie memcgs as well as the "memory.stat" output for all
> of them.
>
> This entails a file at /sys/kernel/debug/zombie_memcgs/all that
> contains a list of zombie memcgs (with indentation to reflect the
> hierarchy) and an id for each of them.
>
> This id can be used to index per-memcg directories at
> /sys/kernel/debug/zombie_memcgs/<id>/, which include debug files. The
> only one we have so far is
> /sys/kernel/debug/zombie_memcgs/<id>/memory.stat.
>
> If there is interest in this, I can share more information.
>
>> ---
>> include/linux/cgroup-defs.h | 1 +
>> kernel/cgroup/cgroup.c | 101 ++++++++++++++++++++++++++++++++++++
>> mm/memcontrol.c | 14 +++++
>> 3 files changed, 116 insertions(+)
>>
>> diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
>> index 8a0d5466c7be..810bd300cbee 100644
>> --- a/include/linux/cgroup-defs.h
>> +++ b/include/linux/cgroup-defs.h
>> @@ -673,6 +673,7 @@ struct cgroup_subsys {
>> void (*exit)(struct task_struct *task);
>> void (*release)(struct task_struct *task);
>> void (*bind)(struct cgroup_subsys_state *root_css);
>> + void (*css_dump)(struct cgroup_subsys_state *css, struct seq_file *m);
>>
>> bool early_init:1;
>>
>> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
>> index 625d7483951c..fb9931ff7570 100644
>> --- a/kernel/cgroup/cgroup.c
>> +++ b/kernel/cgroup/cgroup.c
>> @@ -40,6 +40,7 @@
>> #include <linux/mount.h>
>> #include <linux/pagemap.h>
>> #include <linux/proc_fs.h>
>> +#include <linux/debugfs.h>
>> #include <linux/rcupdate.h>
>> #include <linux/sched.h>
>> #include <linux/sched/task.h>
>> @@ -7068,3 +7069,103 @@ static int __init cgroup_sysfs_init(void)
>> subsys_initcall(cgroup_sysfs_init);
>>
>> #endif /* CONFIG_SYSFS */
>> +
>> +#ifdef CONFIG_DEBUG_FS
>> +void *css_debugfs_seqfile_start(struct seq_file *m, loff_t *pos)
>> +{
>> + struct cgroup_subsys *ss = m->private;
>> + struct cgroup_subsys_state *css;
>> + int id = *pos;
>> +
>> + rcu_read_lock();
>> + css = idr_get_next(&ss->css_idr, &id);
>> + *pos = id;
>> + return css;
>> +}
>> +
>> +void *css_debugfs_seqfile_next(struct seq_file *m, void *v, loff_t *pos)
>> +{
>> + struct cgroup_subsys *ss = m->private;
>> + struct cgroup_subsys_state *css;
>> + int id = *pos + 1;
>> +
>> + css = idr_get_next(&ss->css_idr, &id);
>> + *pos = id;
>> + return css;
>> +}
>> +
>> +void css_debugfs_seqfile_stop(struct seq_file *m, void *v)
>> +{
>> + rcu_read_unlock();
>> +}
>> +
>> +int css_debugfs_seqfile_show(struct seq_file *m, void *v)
>> +{
>> + struct cgroup_subsys *ss = m->private;
>> + struct cgroup_subsys_state *css = v;
>> + /* data is NULL for root cgroup_subsys_state */
>> + struct percpu_ref_data *data = css->refcnt.data;
>> + size_t buflen;
>> + char *buf;
>> + int len;
>> +
>> + seq_printf(m, "css=%pK cgroup=%pK id=%d ino=%lu flags=%#x refcnt=%lu path=",
>> + css, css->cgroup, css->id, cgroup_ino(css->cgroup),
>> + css->flags, data ? atomic_long_read(&data->count) : 0);
>> +
>> + buflen = seq_get_buf(m, &buf);
>> + if (buf) {
>> + len = cgroup_path(css->cgroup, buf, buflen);
>> + seq_commit(m, len < buflen ? len : -1);
>> + }
>> +
>> + if (ss->css_dump) {
>> + seq_puts(m, " -- ");
>> + ss->css_dump(css, m);
>> + }
>> +
>> + seq_putc(m, '\n');
>> + return 0;
>> +}
>> +
>> +static const struct seq_operations css_debug_seq_ops = {
>> + .start = css_debugfs_seqfile_start,
>> + .next = css_debugfs_seqfile_next,
>> + .stop = css_debugfs_seqfile_stop,
>> + .show = css_debugfs_seqfile_show,
>> +};
>> +
>> +static int css_debugfs_open(struct inode *inode, struct file *file)
>> +{
>> + int ret = seq_open(file, &css_debug_seq_ops);
>> + struct seq_file *m = file->private_data;
>> +
>> + if (!ret)
>> + m->private = inode->i_private;
>> + return ret;
>> +}
>> +
>> +static const struct file_operations css_debugfs_fops = {
>> + .open = css_debugfs_open,
>> + .read = seq_read,
>> + .llseek = seq_lseek,
>> + .release = seq_release,
>> +};
>> +
>> +static int __init css_debugfs_init(void)
>> +{
>> + struct cgroup_subsys *ss;
>> + struct dentry *dir;
>> + int ssid;
>> +
>> + dir = debugfs_create_dir("cgroup", NULL);
>> + if (dir) {
>> + for_each_subsys(ss, ssid)
>> + debugfs_create_file(ss->name, 0644, dir, ss,
>> + &css_debugfs_fops);
>> + }
>> +
>> + return 0;
>> +}
>> +late_initcall(css_debugfs_init);
>> +#endif /* CONFIG_DEBUG_FS */
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 4b27e245a055..7b3d4a10ac63 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -5654,6 +5654,20 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
>> }
>> }
>>
>> +static void mem_cgroup_css_dump(struct cgroup_subsys_state *css,
>> + struct seq_file *m)
>> +{
>> + struct mem_cgroup *memcg = mem_cgroup_from_css(css);
>> +
>> + seq_printf(m, "mem_id=%u memory=%lu memsw=%lu kmem=%lu tcpmem=%lu shmem=%lu",
>> + mem_cgroup_id(memcg),
>> + page_counter_read(&memcg->memory),
>> + page_counter_read(&memcg->memsw),
>> + page_counter_read(&memcg->kmem),
>> + page_counter_read(&memcg->tcpmem),
>> + memcg_page_state(memcg, NR_SHMEM));
>> +}
>> +
>> #ifdef CONFIG_MMU
>> /* Handlers for move charge at task migration. */
>> static int mem_cgroup_do_precharge(unsigned long count)
>> --
>> 2.25.1
>>
>>
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