linux-kernel - [PATCH 2/3] memcg: enable accounting for kernfs iattrs

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Date:   Sun, 31 Jul 2022 18:37:27 +0300
From:   Vasily Averin <vvs@...nvz.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org, kernel@...nvz.org,
        Shakeel Butt <shakeelb@...gle.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Michal Koutný <mkoutny@...e.com>,
        Muchun Song <songmuchun@...edance.com>,
        Michal Hocko <mhocko@...e.com>
Subject: [PATCH 2/3] memcg: enable accounting for kernfs iattrs

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
1       32      (simple_xattr_set+0x59)
1       8       (__kernfs_new_node+0x30)

'+' -- to be accounted

This patch enables accounting for kernfs_iattrs_cache slab cache

Signed-off-by: Vasily Averin <vvs@...nvz.org>
Reviewed-by: Roman Gushchin <roman.gushchin@...ux.dev>
Reviewed-by: Michal Koutný <mkoutny@...e.com>
Acked-by: Shakeel Butt <shakeelb@...gle.com>
Reviewed-by: Muchun Song <songmuchun@...edance.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 3ac4191b1c40..40e896c7c86b 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -397,5 +397,6 @@ void __init kernfs_init(void)
 	/* Creates slab cache for kernfs inode attributes */
 	kernfs_iattrs_cache  = kmem_cache_create("kernfs_iattrs_cache",
 					      sizeof(struct kernfs_iattrs),
-					      0, SLAB_PANIC, NULL);
+					      0, SLAB_PANIC | SLAB_ACCOUNT,
+					      NULL);
 }
-- 
2.25.1