From: Qian Cai <cai@lca.pw>
To: Eric Dumazet <eric.dumazet@gmail.com>, davem@davemloft.net
Cc: netdev@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] net/skbuff: silence warnings under memory pressure
Date: Fri, 30 Aug 2019 14:06:55 -0400 [thread overview]
Message-ID: <1567188415.5576.34.camel@lca.pw> (raw)
In-Reply-To: <229ebc3b-1c7e-474f-36f9-0fa603b889fb@gmail.com>
On Fri, 2019-08-30 at 18:15 +0200, Eric Dumazet wrote:
>
> On 8/30/19 5:25 PM, Qian Cai wrote:
> > On Fri, 2019-08-30 at 17:11 +0200, Eric Dumazet wrote:
> > >
> > > On 8/30/19 4:57 PM, Qian Cai wrote:
> > > > When running heavy memory pressure workloads, the system is throwing
> > > > endless warnings below due to the allocation could fail from
> > > > __build_skb(), and the volume of this call could be huge which may
> > > > generate a lot of serial console output and cosumes all CPUs as
> > > > warn_alloc() could be expensive by calling dump_stack() and then
> > > > show_mem().
> > > >
> > > > Fix it by silencing the warning in this call site. Also, it seems
> > > > unnecessary to even print a warning at all if the allocation failed in
> > > > __build_skb(), as it may just retransmit the packet and retry.
> > > >
> > >
> > > Same patches are showing up there and there from time to time.
> > >
> > > Why is this particular spot interesting, against all others not adding
> > > __GFP_NOWARN ?
> > >
> > > Are we going to have hundred of patches adding __GFP_NOWARN at various
> > > points,
> > > or should we get something generic to not flood the syslog in case of
> > > memory
> > > pressure ?
> > >
> >
> > From my testing which uses LTP oom* tests. There are only 3 places need to
> > be
> > patched. The other two are in IOMMU code for both Intel and AMD. The place
> > is
> > particular interesting because it could cause the system with floating
> > serial
> > console output for days without making progress in OOM. I suppose it ends up
> > in
> > a looping condition that warn_alloc() would end up generating more calls
> > into
> > __build_skb() via ksoftirqd.
> >
>
> Yes, but what about other tests done by other people ?
Sigh, I don't know what tests do you have in mind. I tried many memory pressure
tests including LTP, stress-ng, and mmtests etc running for years. I don't
recall see other places that could loop like this for days.
>
> You do not really answer my last question, which was really the point I tried
> to make.
>
> If there is a risk of flooding the syslog, we should fix this generically
> in mm layer, not adding hundred of __GFP_NOWARN all over the places.
>
> Maybe just make __GFP_NOWARN the default, I dunno.
I don't really see how it could end up with adding hundred of _GFP_NOWARN in the
kernel code. If there is really a hundred places could loop like this, it may
make more sense looking into a general solution.
next prev parent reply other threads:[~2019-08-30 18:06 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 [this message]
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
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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