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From: Qian Cai <cai@lca.pw>
To: Eric Dumazet <eric.dumazet@gmail.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Michal Hocko <mhocko@kernel.org>,
	davem@davemloft.net, netdev@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, Petr Mladek <pmladek@suse.com>,
	Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] net/skbuff: silence warnings under memory pressure
Date: Thu, 05 Sep 2019 10:09:15 -0400	[thread overview]
Message-ID: <1567692555.5576.91.camel@lca.pw> (raw)
In-Reply-To: <165827b5-6783-f4f8-69d6-b088dd97eb45@gmail.com>

On Thu, 2019-09-05 at 10:32 +0200, Eric Dumazet wrote:
> 
> On 9/4/19 10:42 PM, Qian Cai wrote:
> 
> > To summary, those look to me are all good long-term improvement that would
> > reduce the likelihood of this kind of livelock in general especially for
> > other
> > unknown allocations that happen while processing softirqs, but it is still
> > up to
> > the air if it fixes it 100% in all situations as printk() is going to take
> > more
> > time and could deal with console hardware that involve irq_exit() anyway.
> > 
> > On the other hand, adding __GPF_NOWARN in the build_skb() allocation will
> > fix
> > this known NET_TX_SOFTIRQ case which is common when softirqd involved at
> > least
> > in short-term. It even have a benefit to reduce the overall warn_alloc()
> > noise
> > out there.
> > 
> > I can resubmit with an update changelog. Does it make any sense?
> 
> It does not make sense.
> 
> We have thousands other GFP_ATOMIC allocations in the networking stacks.

Instead of repeatedly make generalize statements, could you enlighten me with
some concrete examples that have the similar properties which would trigger a
livelock,

- guaranteed GFP_ATOMIC allocations when processing softirq batches.
- the allocation has a fallback mechanism that is unnecessary to warn a failure.

I thought "skb" is a special-case here as every packet sent or received is
handled using this data structure.

> 
> Soon you will have to send more and more patches adding __GFP_NOWARN once
> your workloads/tests can hit all these various points.

I doubt so.

> 
> It is really time to fix this problem generically, instead of having
> to review hundreds of patches.
> 
> This was my initial feedback really, nothing really has changed since.

I feel like you may not follow the thread closely. There are more details
uncovered in the last few days and narrowed down to the culprits.

> 
> The ability to send a warning with a stack trace, holding the cpu
> for many milliseconds should not be decided case by case, otherwise
> every call points will decide to opt-out from the harmful warnings.

That is not really the reasons anymore why I asked to add a __GPF_NOWARN here.

  reply	other threads:[~2019-09-05 14:15 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-30 14:57 [PATCH] net/skbuff: silence warnings under memory pressure Qian Cai
2019-08-30 15:11 ` Eric Dumazet
2019-08-30 15:25   ` Qian Cai
2019-08-30 16:15     ` Eric Dumazet
2019-08-30 18:06       ` Qian Cai
2019-09-03 13:22       ` Michal Hocko
2019-09-03 15:42         ` Qian Cai
2019-09-03 18:53           ` Michal Hocko
2019-09-03 21:42             ` Qian Cai
2019-09-04  6:15               ` Michal Hocko
2019-09-04  6:41                 ` Sergey Senozhatsky
2019-09-04  6:54                   ` Michal Hocko
2019-09-04  7:19                     ` Sergey Senozhatsky
2019-09-04  7:43                       ` Sergey Senozhatsky
2019-09-04 12:14                         ` Qian Cai
2019-09-04 14:48                           ` Sergey Senozhatsky
2019-09-04 15:07                             ` Qian Cai
2019-09-04 20:42                             ` Qian Cai
2019-09-05  8:32                               ` Eric Dumazet
2019-09-05 14:09                                 ` Qian Cai [this message]
2019-09-05 15:06                                   ` Eric Dumazet
2019-09-05 15:14                                   ` Eric Dumazet
2019-09-05 11:32                               ` Sergey Senozhatsky
2019-09-05 16:03                                 ` Qian Cai
2019-09-05 17:14                                   ` Steven Rostedt
2019-09-06  2:50                                     ` Sergey Senozhatsky
2019-09-06  4:32                                   ` Sergey Senozhatsky
2019-09-06 21:17                                     ` Qian Cai
2019-09-05 17:23                                 ` Steven Rostedt
2019-09-06  3:39                                   ` Sergey Senozhatsky
2019-09-06 15:32                                     ` Petr Mladek
2019-09-09  1:10                                       ` Sergey Senozhatsky
2019-09-06 14:55                                 ` Petr Mladek
2019-09-06 19:51                                   ` Sergey Senozhatsky
2019-11-14 17:12                                 ` Qian Cai
2019-11-18 15:27                                   ` Petr Mladek
2019-11-19  0:41                                     ` Sergey Senozhatsky
2019-11-19  9:41                                       ` Petr Mladek
2019-11-19 15:58                                         ` Qian Cai
2019-11-20  1:30                                         ` Sergey Senozhatsky
2019-11-20 16:13                                           ` Petr Mladek
2019-11-21  1:05                                             ` Sergey Senozhatsky
2019-11-21  9:15                                               ` Petr Mladek
2019-09-04  7:00                   ` Sergey Senozhatsky
2019-09-04  8:25                     ` Michal Hocko
2019-09-04 11:59                       ` Qian Cai
2019-09-04 12:07                         ` Michal Hocko
2019-09-04 12:28                           ` Qian Cai
2019-09-07 11:00                       ` Tetsuo Handa
2019-09-04  6:15               ` Michal Hocko
2019-09-02 14:24     ` Vlastimil Babka

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