[PATCH 3/3] memcg: enable accounting for struct simple_xattr

[Vasily Averin]

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 struct simple_xattr.
In described scenaro this structire was allocated directly during
kernfs creation for selinux label. Even here it consumes noticeable
part of newly allocated object.
However please keep in mind that xattr can be allocated later,
via setxattr system calls, its size is controlled by userspace
and can reach 64Kb per call. kernfs objects lives in memory,
so it is improtant to account it.

Signed-off-by: Vasily Averin <vvs@xxxxxxxxxx>
Reviewed-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx>
Acked-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 fs/xattr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xattr.c b/fs/xattr.c
index e8dd03e4561e..98dcf6600bd9 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -1001,7 +1001,7 @@ struct simple_xattr *simple_xattr_alloc(const void *value, size_t size)
 	if (len < sizeof(*new_xattr))
 		return NULL;
 
-	new_xattr = kvmalloc(len, GFP_KERNEL);
+	new_xattr = kvmalloc(len, GFP_KERNEL_ACCOUNT);
 	if (!new_xattr)
 		return NULL;
 
-- 
2.25.1