[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <20231013010921.qa4o6nsqjkndsyb5@google.com>
Date: Fri, 13 Oct 2023 01:09:21 +0000
From: Shakeel Butt <shakeelb@...gle.com>
To: Abel Wu <wuyun.abel@...edance.com>
Cc: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Kuniyuki Iwashima <kuniyu@...zon.com>,
Breno Leitao <leitao@...ian.org>,
Alexander Mikhalitsyn <alexander@...alicyn.com>,
David Howells <dhowells@...hat.com>,
Jason Xing <kernelxing@...cent.com>,
Xin Long <lucien.xin@...il.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujtsu.com>,
"open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 2/2] sock: Fix improper heuristic on raising memory
On Tue, Oct 03, 2023 at 08:49:08PM +0800, Abel Wu wrote:
[...]
> > 1. minimum buffer size even under pressure.
>
> This is required by RFC 7323 (TCP Extensions for High Performance) to
> make features like Window Scale option work as expected, and should be
> succeeded under global pressure by tcp_{r,w}mem's definition. And IMHO
> for same reason, it should also be succeeded under memcg pressure, or
> else workloads might suffer performance drop due to bottleneck on
> network.
>
> The allocation must not be succeeded either exceed global or memcg's
> hard limit, or else a DoS attack can be taken place by spawning lots
> of sockets that are under minimum buffer size.
>
Sounds good.
> >
> > 2. allow allocation for a socket whose usage is below average of the
> > system.
>
> Since 'average' is within the scope of global accounting, this one
> only makes sense under global memory pressure. Actually this exists
> before cgroup was born, hence doesn't take memcg into consideration.
>
> While OTOH the intention of throttling under memcg pressure is to
> relief the memcg from heavy reclaim pressure, this heuristic does no
> help. And there also seems to be no reason to succeed the allocation
> when global or memcg's hard limit is exceeded.
>
Sounds good too.
> >
> > 3. socket is over its sndbuf.
>
> TBH I don't get its point..
>
So, this corresponds to following code in __sk_mem_raise_allocated()
if (kind == SK_MEM_SEND && sk->sk_type == SOCK_STREAM) {
sk_stream_moderate_sndbuf(sk);
/* Fail only if socket is _under_ its sndbuf.
* In this case we cannot block, so that we have to fail.
*/
if (sk->sk_wmem_queued + size >= sk->sk_sndbuf) {
/* Force charge with __GFP_NOFAIL */
if (memcg_charge && !charged) {
mem_cgroup_charge_skmem(sk->sk_memcg, amt,
gfp_memcg_charge() | __GFP_NOFAIL);
}
return 1;
}
}
Here we moderate the sk_sndbuf possibly half of sk_wmem_queued and thus
we always succeed unless user has done SO_SNDBUF on the socket in which
case it interacts with sk_stream_wait_memory() called in sendmsg.
I am not really able to make sense of the interaction between this code
and sk_stream_wait_memory() and will punt to networking experts to shed
some light.
Other than that I think we need to answer if we want to moderate the
sndbuf on memcg charge failure.
> >
> > Let's discuss which heuristic applies to which accounting infra and
> > under which state (under pressure or over limit).
>
> I will follow your suggestion to post a patch to explicitly document
> the behaviors once things are cleared.
>
Let's just post the patch and see what other folks comment as well.
Powered by blists - more mailing lists