netdev - Re: [PATCH 3/3] net: introduce res_counter_charge

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Message-ID: <20120124081552.GB1660@cmpxchg.org>
Date:	Tue, 24 Jan 2012 09:15:52 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	Glauber Costa <glommer@...allels.com>
Cc:	davem@...emloft.net, linux-kernel@...r.kernel.org,
	kamezawa.hiroyu@...fujitsu.com, netdev@...r.kernel.org,
	eric.dumazet@...il.com, cgroups@...r.kernel.org,
	Michal Hocko <mhocko@...e.cz>, Tejun Heo <tj@...nel.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Laurent Chavey <chavey@...gle.com>
Subject: Re: [PATCH 3/3] net: introduce res_counter_charge_nofail() for
 socket allocations

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@...allels.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...e.cz>
> CC: Tejun Heo <tj@...nel.org>
> CC: Li Zefan <lizf@...fujitsu.com>
> CC: Laurent Chavey <chavey@...gle.com>

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