Re: [PATCH 3/3] net: introduce res_counter_charge_nofail() for socket allocations

[Johannes Weiner <hannes@cmpxchg.org>]

On Fri, Jan 20, 2012 at 06:57:16PM +0400, Glauber Costa wrote:
> There is a case in __sk_mem_schedule(), where an allocation
> is beyond the maximum, but yet we are allowed to proceed.
> It happens under the following condition:
> 
> 	sk->sk_wmem_queued + size >= sk->sk_sndbuf
> 
> The network code won't revert the allocation in this case,
> meaning that at some point later it'll try to do it. Since
> this is never communicated to the underlying res_counter
> code, there is an inbalance in res_counter uncharge operation.
> 
> I see two ways of fixing this:
> 
> 1) storing the information about those allocations somewhere
>    in memcg, and then deducting from that first, before
>    we start draining the res_counter,
> 2) providing a slightly different allocation function for
>    the res_counter, that matches the original behavior of
>    the network code more closely.
> 
> I decided to go for #2 here, believing it to be more elegant,
> since #1 would require us to do basically that, but in a more
> obscure way.
> 
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@suse.cz>
> CC: Tejun Heo <tj@kernel.org>
> CC: Li Zefan <lizf@cn.fujitsu.com>
> CC: Laurent Chavey <chavey@google.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>