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Message-ID: <CAJD7tkYM0JBukPMWCWtx-nrzGgPw4Y6m1p2_Ynb9fzSgsS0igg@mail.gmail.com>
Date: Mon, 11 Sep 2023 15:16:28 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: "Yakunin, Dmitry (Nebius)" <zeil@...ius.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
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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