Re: [RFC PATCH 1/3] cgroup: list all subsystem states in debugfs files

[Dmitry Yakunin <zeil@xxxxxxxxxx>]

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@xxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> > Reviewed-by: Andrey Ryabinin <arbn@xxxxxxxxxxxxxxx>
> > Signed-off-by: Dmitry Yakunin <zeil@xxxxxxxxxx>
> 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