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From:   Vasily Averin <vvs@virtuozzo.com>
Subject: [PATCH v7 01/10] memcg: enable accounting for mnt_cache entries
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     cgroups@vger.kernel.org, Michal Hocko <mhocko@kernel.org>,
        Shakeel Butt <shakeelb@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Roman Gushchin <guro@fb.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
References: <6f21a0e0-bd36-b6be-1ffa-0dc86c06c470@virtuozzo.com>
 <cover.1627362057.git.vvs@virtuozzo.com>
Message-ID: <045db11f-4a45-7c9b-2664-5b32c2b44943@virtuozzo.com>
Date:   Tue, 27 Jul 2021 08:33:12 +0300
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The kernel allocates ~400 bytes of 'strcut mount' for any new mount.
Creating a new mount namespace clones most of the parent mounts,
and this can be repeated many times. Additionally, each mount allocates
up to PATH_MAX=4096 bytes for mnt->mnt_devname.

It makes sense to account for these allocations to restrict the host's
memory consumption from inside the memcg-limited container.

Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
---
 fs/namespace.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index ab4174a..c6a74e5 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -203,7 +203,8 @@ static struct mount *alloc_vfsmnt(const char *name)
 			goto out_free_cache;
 
 		if (name) {
-			mnt->mnt_devname = kstrdup_const(name, GFP_KERNEL);
+			mnt->mnt_devname = kstrdup_const(name,
+							 GFP_KERNEL_ACCOUNT);
 			if (!mnt->mnt_devname)
 				goto out_free_id;
 		}
@@ -4222,7 +4223,7 @@ void __init mnt_init(void)
 	int err;
 
 	mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct mount),
-			0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
+			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
 
 	mount_hashtable = alloc_large_system_hash("Mount-cache",
 				sizeof(struct hlist_head),
-- 
1.8.3.1