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Date:   Fri, 13 May 2022 18:51:41 +0300
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From:   Vasily Averin <vvs@openvz.org>
Subject: [PATCH 1/4] memcg: enable accounting for large allocations in
 mem_cgroup_css_alloc
To:     Roman Gushchin <roman.gushchin@linux.dev>,
        Shakeel Butt <shakeelb@google.com>,
        =?UTF-8?Q?Michal_Koutn=c3=bd?= <mkoutny@suse.com>
Cc:     kernel@openvz.org, linux-kernel@vger.kernel.org,
        Vlastimil Babka <vbabka@suse.cz>,
        Michal Hocko <mhocko@suse.com>, cgroups@vger.kernel.org
References: <Ynv7+VG+T2y9rpdk@carbon>
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In-Reply-To: <Ynv7+VG+T2y9rpdk@carbon>
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cgroup mkdir can be misused inside memcg limited container. It can allocate
a lot of host memory without memcg accounting, cause global memory shortage
and force OOM to kill random host process.

Below [1] is result of mkdir /sys/fs/cgroup/test tracing on VM with 4 cpus

number	bytes	$1*$2	sum	note	call_site
of	alloc
allocs
------------------------------------------------------------
1       14448   14448   14448   =       percpu_alloc_percpu:
1       8192    8192    22640           (mem_cgroup_css_alloc+0x54)
49      128     6272    28912           (__kernfs_new_node+0x4e)
49      96      4704    33616           (simple_xattr_alloc+0x2c)
49      88      4312    37928           (__kernfs_iattrs+0x56)
1       4096    4096    42024           (cgroup_mkdir+0xc7)
1       3840    3840    45864   =       percpu_alloc_percpu:
4       512     2048    47912           (alloc_fair_sched_group+0x166)
4       512     2048    49960           (alloc_fair_sched_group+0x139)
1       2048    2048    52008           (mem_cgroup_css_alloc+0x109)
	[smaller objects skipped]
---
Total			61728

'=' --  accounted allocations

This patch enabled accounting for one of the main memory hogs in this
experiment: allocation which are called inside mem_cgroup_css_alloc()

Signed-off-by: Vasily Averin <vvs@openvz.org>
Link: [1] https://lore.kernel.org/all/1aa4cd22-fcb6-0e8d-a1c6-23661d618864@openvz.org/
---
 mm/memcontrol.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 598fece89e2b..52c6163ba6dc 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5031,7 +5031,7 @@ static int alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
 {
 	struct mem_cgroup_per_node *pn;
 
-	pn = kzalloc_node(sizeof(*pn), GFP_KERNEL, node);
+	pn = kzalloc_node(sizeof(*pn), GFP_KERNEL_ACCOUNT, node);
 	if (!pn)
 		return 1;
 
@@ -5083,7 +5083,7 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
 	int __maybe_unused i;
 	long error = -ENOMEM;
 
-	memcg = kzalloc(struct_size(memcg, nodeinfo, nr_node_ids), GFP_KERNEL);
+	memcg = kzalloc(struct_size(memcg, nodeinfo, nr_node_ids), GFP_KERNEL_ACCOUNT);
 	if (!memcg)
 		return ERR_PTR(error);
 
-- 
2.31.1