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Date:   Mon, 30 May 2022 14:26:00 +0300
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From:   Vasily Averin <vvs@openvz.org>
Subject: [PATCH mm v3 2/9] memcg: enable accounting for kernfs nodes
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     kernel@openvz.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Shakeel Butt <shakeelb@google.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        =?UTF-8?Q?Michal_Koutn=c3=bd?= <mkoutny@suse.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Michal Hocko <mhocko@suse.com>,
        Muchun Song <songmuchun@bytedance.com>, cgroups@vger.kernel.org
References: <06505918-3b8a-0ad5-5951-89ecb510138e@openvz.org>
 <cover.1653899364.git.vvs@openvz.org>
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Precedence: bulk

kernfs nodes are quite small kernel objects, however there are few
scenarios where it consumes significant piece of all allocated memory:

1) creating a new netdevice allocates ~50Kb of memory, where ~10Kb
   was allocated for 80+ kernfs nodes.

2) cgroupv2 mkdir allocates ~60Kb of memory, ~10Kb of them are kernfs
   structures.

3) Shakeel Butt reports that Google has workloads which create 100s
   of subcontainers and they have observed high system overhead
   without memcg accounting of kernfs.

Usually new kernfs node creates few other objects:

Allocs  Alloc   Allocation
number  size
--------------------------------------------
1   +  128      (__kernfs_new_node+0x4d)	kernfs node
1   +   88      (__kernfs_iattrs+0x57)		kernfs iattrs
1   +   96      (simple_xattr_alloc+0x28)	simple_xattr, can grow over 4Kb
1       32      (simple_xattr_set+0x59)
1       8       (__kernfs_new_node+0x30)

'+' -- to be accounted

This patch enables accounting for kernfs nodes slab cache.

Signed-off-by: Vasily Averin <vvs@openvz.org>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Reviewed-by: Michal Koutný <mkoutny@suse.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
---
 fs/kernfs/mount.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index cfa79715fc1a..3ac4191b1c40 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -391,7 +391,8 @@ void __init kernfs_init(void)
 {
 	kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
 					      sizeof(struct kernfs_node),
-					      0, SLAB_PANIC, NULL);
+					      0, SLAB_PANIC | SLAB_ACCOUNT,
+					      NULL);
 
 	/* Creates slab cache for kernfs inode attributes */
 	kernfs_iattrs_cache  = kmem_cache_create("kernfs_iattrs_cache",
-- 
2.36.1