Commit 4a07c222 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: replace "cgroup.populated" with "cgroup.events" 



memcg already uses "memory.events" for event reporting and other
controllers may need event reporting too.  Let's standardize on
"$SUBSYS.events" interface file for reporting events which don't
happen too frequently and thus can share event notification.

"cgroup.populated" is replaced with "populated" field in
"cgroup.events" and documentation is updated accordingly.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
parent 9e10a130

Documentation/cgroups/unified-hierarchy.txt

+10 −5
Original line number Diff line number Diff line
@@ -341,11 +341,11 @@ is riddled with issues. 
  unnecessarily complicated and probably done this way because event

  delivery itself was expensive.



Unified hierarchy implements an interface file "cgroup.populated"

which can be used to monitor whether the cgroup's subhierarchy has

tasks in it or not.  Its value is 0 if there is no task in the cgroup

and its descendants; otherwise, 1.  poll and [id]notify events are

triggered when the value changes.

Unified hierarchy implements "populated" field in "cgroup.events"

interface file which can be used to monitor whether the cgroup's

subhierarchy has tasks in it or not.  Its value is 0 if there is no

task in the cgroup and its descendants; otherwise, 1.  poll and

[id]notify events are triggered when the value changes.



This is significantly lighter and simpler and trivially allows

delegating management of subhierarchy - subhierarchy monitoring can
@@ -435,6 +435,11 @@ may be specified in any order and not all pairs have to be specified. 
  the first entry in the file.  Specific entries can use "default" as

  its value to indicate inheritance of the default value.



- For events which are not very high frequency, an interface file

  "events" should be created which lists event key value pairs.

  Whenever a notifiable event happens, file modified event should be

  generated on the file.





5-4. Per-Controller Changes

include/linux/cgroup-defs.h

+1 −1
Original line number Diff line number Diff line
@@ -226,7 +226,7 @@ struct cgroup { 


	struct kernfs_node *kn;		/* cgroup kernfs entry */

	struct kernfs_node *procs_kn;	/* kn for "cgroup.procs" */

	struct kernfs_node *populated_kn; /* kn for "cgroup.subtree_populated" */

	struct kernfs_node *events_kn;	/* kn for "cgroup.events" */



	/*

	 * The bitmask of subsystems enabled on the child cgroups.

kernel/cgroup.c

+9 −8
Original line number Diff line number Diff line
@@ -611,8 +611,8 @@ static void cgroup_update_populated(struct cgroup *cgrp, bool populated) 
		if (!trigger)

			break;



		if (cgrp->populated_kn)

			kernfs_notify(cgrp->populated_kn);

		if (cgrp->events_kn)

			kernfs_notify(cgrp->events_kn);

		cgrp = cgroup_parent(cgrp);

	} while (cgrp);

}
@@ -3045,9 +3045,10 @@ err_undo_css: 
	goto out_unlock;

}



static int cgroup_populated_show(struct seq_file *seq, void *v)

static int cgroup_events_show(struct seq_file *seq, void *v)

{

	seq_printf(seq, "%d\n", (bool)seq_css(seq)->cgroup->populated_cnt);

	seq_printf(seq, "populated %d\n",

		   (bool)seq_css(seq)->cgroup->populated_cnt);

	return 0;

}
@@ -3214,8 +3215,8 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cftype *cft) 


	if (cft->write == cgroup_procs_write)

		cgrp->procs_kn = kn;

	else if (cft->seq_show == cgroup_populated_show)

		cgrp->populated_kn = kn;

	else if (cft->seq_show == cgroup_events_show)

		cgrp->events_kn = kn;

	return 0;

}
@@ -4388,9 +4389,9 @@ static struct cftype cgroup_dfl_base_files[] = { 
		.write = cgroup_subtree_control_write,

	},

	{

		.name = "cgroup.populated",

		.name = "cgroup.events",

		.flags = CFTYPE_NOT_ON_ROOT,

		.seq_show = cgroup_populated_show,

		.seq_show = cgroup_events_show,

	},

	{ }	/* terminate */

};

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