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From: =?UTF-8?q?Michal=20Koutn=C3=BD?= <mkoutny@suse.com>
To: cgroups@vger.kernel.org,
	linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-kselftest@vger.kernel.org
Cc: Tejun Heo <tj@kernel.org>,
	Zefan Li <lizefan.x@bytedance.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Shuah Khan <shuah@kernel.org>,
	Muhammad Usama Anjum <usama.anjum@collabora.com>
Subject: [PATCH v4 4/6] cgroup/pids: Add pids.events.local
Date: Tue, 16 Apr 2024 16:20:12 +0200
Message-ID: <20240416142014.27630-5-mkoutny@suse.com>
In-Reply-To: <20240416142014.27630-1-mkoutny@suse.com>
References: <20240416142014.27630-1-mkoutny@suse.com>
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Hierarchical counting of events is not practical for watching when a
particular pids.max is being hit. Therefore introduce .local flavor of
events file (akin to memory controller) that collects only events
relevant to given cgroup.

The file is only added to the default hierarchy.

Signed-off-by: Michal Koutný <mkoutny@suse.com>
---
 kernel/cgroup/pids.c | 88 +++++++++++++++++++++++++++++++++++---------
 1 file changed, 71 insertions(+), 17 deletions(-)

diff --git a/kernel/cgroup/pids.c b/kernel/cgroup/pids.c
index 4ad28109c1c8..6cd15c3785d4 100644
--- a/kernel/cgroup/pids.c
+++ b/kernel/cgroup/pids.c
@@ -57,10 +57,12 @@ struct pids_cgroup {
 	atomic64_t			limit;
 	int64_t				watermark;
 
-	/* Handle for "pids.events" */
+	/* Handles for pids.events[.local] */
 	struct cgroup_file		events_file;
+	struct cgroup_file		events_local_file;
 
 	atomic64_t			events[NR_PIDCG_EVENTS];
+	atomic64_t			events_local[NR_PIDCG_EVENTS];
 };
 
 static struct pids_cgroup *css_pids(struct cgroup_subsys_state *css)
@@ -244,21 +246,23 @@ static void pids_event(struct pids_cgroup *pids_forking,
 	struct pids_cgroup *p = pids_forking;
 	bool limit = false;
 
-	for (; parent_pids(p); p = parent_pids(p)) {
-		/* Only log the first time limit is hit. */
-		if (atomic64_inc_return(&p->events[PIDCG_FORKFAIL]) == 1) {
-			pr_info("cgroup: fork rejected by pids controller in ");
-			pr_cont_cgroup_path(p->css.cgroup);
-			pr_cont("\n");
-		}
-		cgroup_file_notify(&p->events_file);
-
-		if (!cgroup_subsys_on_dfl(pids_cgrp_subsys) ||
-		    cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS)
-			break;
+	/* Only log the first time limit is hit. */
+	if (atomic64_inc_return(&p->events_local[PIDCG_FORKFAIL]) == 1) {
+		pr_info("cgroup: fork rejected by pids controller in ");
+		pr_cont_cgroup_path(p->css.cgroup);
+		pr_cont("\n");
+	}
+	cgroup_file_notify(&p->events_local_file);
+	if (!cgroup_subsys_on_dfl(pids_cgrp_subsys) ||
+	    cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS)
+		return;
 
-		if (p == pids_over_limit)
+	for (; parent_pids(p); p = parent_pids(p)) {
+		if (p == pids_over_limit) {
 			limit = true;
+			atomic64_inc(&p->events_local[PIDCG_MAX]);
+			cgroup_file_notify(&p->events_local_file);
+		}
 		if (limit)
 			atomic64_inc(&p->events[PIDCG_MAX]);
 
@@ -368,20 +372,68 @@ static s64 pids_peak_read(struct cgroup_subsys_state *css,
 	return READ_ONCE(pids->watermark);
 }
 
-static int pids_events_show(struct seq_file *sf, void *v)
+static int __pids_events_show(struct seq_file *sf, bool local)
 {
 	struct pids_cgroup *pids = css_pids(seq_css(sf));
 	enum pidcg_event pe = PIDCG_MAX;
+	atomic64_t *events;
 
 	if (!cgroup_subsys_on_dfl(pids_cgrp_subsys) ||
-	    cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS)
+	    cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS) {
 		pe = PIDCG_FORKFAIL;
+		local = true;
+	}
+	events = local ? pids->events_local : pids->events;
 
-	seq_printf(sf, "max %lld\n", (s64)atomic64_read(&pids->events[pe]));
+	seq_printf(sf, "max %lld\n", (s64)atomic64_read(&events[pe]));
+	return 0;
+}
+
+static int pids_events_show(struct seq_file *sf, void *v)
+{
+	__pids_events_show(sf, false);
+	return 0;
+}
+
+static int pids_events_local_show(struct seq_file *sf, void *v)
+{
+	__pids_events_show(sf, true);
 	return 0;
 }
 
 static struct cftype pids_files[] = {
+	{
+		.name = "max",
+		.write = pids_max_write,
+		.seq_show = pids_max_show,
+		.flags = CFTYPE_NOT_ON_ROOT,
+	},
+	{
+		.name = "current",
+		.read_s64 = pids_current_read,
+		.flags = CFTYPE_NOT_ON_ROOT,
+	},
+	{
+		.name = "peak",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.read_s64 = pids_peak_read,
+	},
+	{
+		.name = "events",
+		.seq_show = pids_events_show,
+		.file_offset = offsetof(struct pids_cgroup, events_file),
+		.flags = CFTYPE_NOT_ON_ROOT,
+	},
+	{
+		.name = "events.local",
+		.seq_show = pids_events_local_show,
+		.file_offset = offsetof(struct pids_cgroup, events_local_file),
+		.flags = CFTYPE_NOT_ON_ROOT,
+	},
+	{ }	/* terminate */
+};
+
+static struct cftype pids_files_legacy[] = {
 	{
 		.name = "max",
 		.write = pids_max_write,
@@ -407,6 +459,7 @@ static struct cftype pids_files[] = {
 	{ }	/* terminate */
 };
 
+
 struct cgroup_subsys pids_cgrp_subsys = {
 	.css_alloc	= pids_css_alloc,
 	.css_free	= pids_css_free,
@@ -416,5 +469,6 @@ struct cgroup_subsys pids_cgrp_subsys = {
 	.cancel_fork	= pids_cancel_fork,
 	.release	= pids_release,
 	.dfl_cftypes	= pids_files,
+	.legacy_cftypes = pids_files_legacy,
 	.threaded	= true,
 };
-- 
2.44.0