[RFC] slub: show dead memcg caches in a separate file

* [RFC] slub: show dead memcg caches in a separate file
@ 2012-05-03 18:47 ` Glauber Costa
  0 siblings, 0 replies; 9+ messages in thread
From: Glauber Costa @ 2012-05-03 18:47 UTC (permalink / raw)
  To: cgroups
  Cc: linux-mm, devel, Glauber Costa, Christoph Lameter, Pekka Enberg,
	Michal Hocko, Kamezawa Hiroyuki, Johannes Weiner,
	Suleiman Souhlal, Frederic Weisbecker

One of the very few things that still unsettles me in the kmem
controller for memcg, is how badly we mess up with the
/proc/slabinfo file.

It is alright to have the cgroup caches listed in slabinfo, but once
they die, I think they should be removed right away. A box full
of containers that come and go will rapidly turn that file into
a supreme mess. However, we currently leave them there so we can
determine where our used memory currently is.

This patch attempts to clean this up by creating a separate proc file
only to handle the dead slabs. Among other advantages, we need a lot
less information in a dead cache: only its current size in memory
matters to us.

So besides avoiding polution of the slabinfo files, we can access
dead cache information itself in a cleaner way.

I implemented this as a proof of concept while finishing up
my last round for submission. But I am sending this separately
to collect opinions from all of you. I can either implement
a version of this for the slab, or follow any other route.

Thanks

Signed-off-by: Glauber Costa <glommer@parallels.com>
CC: Christoph Lameter <cl@linux.com>
CC: Pekka Enberg <penberg@cs.helsinki.fi>
CC: Michal Hocko <mhocko@suse.cz>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
CC: Johannes Weiner <hannes@cmpxchg.org>
CC: Suleiman Souhlal <suleiman@google.com>
CC: Frederic Weisbecker <fweisbec@gmail.com>
---
 include/linux/slab.h |    3 ++
 mm/slub.c            |   82 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 85 insertions(+), 0 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 5df00c1..d6a0cf4 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -171,6 +171,9 @@ struct mem_cgroup_cache_params {
 #endif
 	struct list_head destroyed_list; /* Used when deleting cpuset cache */
 };
+
+extern void memcg_finish_slab_destruction(void);
+extern void memcg_start_slab_destruction(void);
 #endif
 
 /*
diff --git a/mm/slub.c b/mm/slub.c
index 0652e99..de066e3 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5657,6 +5657,11 @@ static int s_show(struct seq_file *m, void *p)
 
 	s = list_entry(p, struct kmem_cache, list);
 
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
+	if (s->memcg_params.dead)
+		return 0;
+#endif
+
 	for_each_online_node(node) {
 		struct kmem_cache_node *n = get_node(s, node);
 
@@ -5688,6 +5693,83 @@ static const struct seq_operations slabinfo_op = {
 	.show = s_show,
 };
 
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
+static void *s_start_dead(struct seq_file *m, loff_t *pos)
+{
+	loff_t n = *pos;
+
+	down_read(&slub_lock);
+	if (!n) {
+		seq_puts(m, "slab_name                               ");
+		seq_puts(m, "pagesperslab num_slabs");
+		seq_putc(m, '\n');
+	}
+
+	return seq_list_start(&slab_caches, *pos);
+}
+
+static int s_show_dead(struct seq_file *m, void *p)
+{
+	unsigned long nr_slabs = 0;
+	struct kmem_cache *s;
+	int node;
+
+	s = list_entry(p, struct kmem_cache, list);
+
+	if (!s->memcg_params.dead)
+		return 0;
+
+	for_each_online_node(node) {
+		struct kmem_cache_node *n = get_node(s, node);
+
+		if (!n)
+			continue;
+
+		nr_slabs += atomic_long_read(&n->nr_slabs);
+	}
+
+	seq_printf(m, "%-40s %11d", s->name, (1 << oo_order(s->oo)));
+	seq_printf(m, " %9lu", nr_slabs);
+	seq_putc(m, '\n');
+	return 0;
+}
+
+
+static const struct seq_operations dead_slabinfo_op = {
+	.start = s_start_dead,
+	.next = s_next,
+	.stop = s_stop,
+	.show = s_show_dead,
+};
+
+static int dead_slabinfo_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &dead_slabinfo_op);
+}
+
+static const struct file_operations proc_dead_slabinfo_operations = {
+	.open		= dead_slabinfo_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
+static atomic_t dead_memcg_counter;
+
+void memcg_start_slab_destruction(void)
+{
+	if (atomic_add_return(1, &dead_memcg_counter) == 1)
+		proc_create("dead_slabinfo", S_IRUSR, NULL,
+			    &proc_dead_slabinfo_operations);
+}
+
+void memcg_finish_slab_destruction(void)
+{
+	if (atomic_dec_and_test(&dead_memcg_counter))
+		remove_proc_entry("dead_slabinfo", NULL);
+}
+#endif
+
 static int slabinfo_open(struct inode *inode, struct file *file)
 {
 	return seq_open(file, &slabinfo_op);
-- 
1.7.7.6

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

^ permalink raw reply related	[flat|nested] 9+ messages in thread