[Devel] Re: [PATCH v5 6/8] tcp buffer limitation: per-cgroup limit

[Eric Dumazet]

Le mardi 04 octobre 2011 à 16:17 +0400, Glauber Costa a écrit :
> This patch uses the "tcp_max_mem" field of the kmem_cgroup to
> effectively control the amount of kernel memory pinned by a cgroup.
> 
> We have to make sure that none of the memory pressure thresholds
> specified in the namespace are bigger than the current cgroup.
> 
> Signed-off-by: Glauber Costa <glommer at parallels.com>
> CC: David S. Miller <davem at davemloft.net>
> CC: Hiroyouki Kamezawa <kamezawa.hiroyu at jp.fujitsu.com>
> CC: Eric W. Biederman <ebiederm at xmission.com>
> ---


> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -256,6 +256,7 @@ extern int sysctl_tcp_thin_dupack;
>  struct mem_cgroup;
>  struct tcp_memcontrol {
>  	/* per-cgroup tcp memory pressure knobs */
> +	int tcp_max_memory;
>  	atomic_long_t tcp_memory_allocated;
>  	struct percpu_counter tcp_sockets_allocated;
>  	/* those two are read-mostly, leave them at the end */
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c

So tcp_max_memory is an "int".


> +static u64 tcp_read_limit(struct cgroup *cgrp, struct cftype *cft)
> +{
> +	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> +	return memcg->tcp.tcp_max_memory << PAGE_SHIFT;
> +}

1) Typical integer overflow here.

You need :

return ((u64)memcg->tcp.tcp_max_memory) << PAGE_SHIFT;


2) Could you add const qualifiers when possible to your pointers ?