linux-kernel - [PATCH mm v2 4/9] memcg: enable accounting for struct simple

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Message-ID: <b69d2389-3a1f-d0bb-6a14-83473fe2d815@openvz.org>
Date:   Sat, 21 May 2022 19:38:11 +0300
From:   Vasily Averin <vvs@...nvz.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     kernel@...nvz.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Shakeel Butt <shakeelb@...gle.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Michal Koutný <mkoutny@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>, cgroups@...r.kernel.org
Subject: [PATCH mm v2 4/9] memcg: enable accounting for struct simple_xattr

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. Size of this
structure depends on userspace and can grow over 4Kb.

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>
---
 fs/xattr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xattr.c b/fs/xattr.c
index 998045165916..31305b941756 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -950,7 +950,7 @@ 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;
 
-- 
2.36.1