Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 4 Sep 2019 15:41:44 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To:     Michal Hocko <mhocko@kernel.org>
Cc:     Qian Cai <cai@lca.pw>, Eric Dumazet <eric.dumazet@gmail.com>,
        davem@davemloft.net, netdev@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] net/skbuff: silence warnings under memory pressure
Message-ID: <20190904064144.GA5487@jagdpanzerIV>
References: <1567177025-11016-1-git-send-email-cai@lca.pw>
 <6109dab4-4061-8fee-96ac-320adf94e130@gmail.com>
 <1567178728.5576.32.camel@lca.pw>
 <229ebc3b-1c7e-474f-36f9-0fa603b889fb@gmail.com>
 <20190903132231.GC18939@dhcp22.suse.cz>
 <1567525342.5576.60.camel@lca.pw>
 <20190903185305.GA14028@dhcp22.suse.cz>
 <1567546948.5576.68.camel@lca.pw>
 <20190904061501.GB3838@dhcp22.suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20190904061501.GB3838@dhcp22.suse.cz>
User-Agent: Mutt/1.12.1 (2019-06-15)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On (09/04/19 08:15), Michal Hocko wrote:
> > If you look at the original report, the failed allocation dump_stack() is,
> > 
> > ?<IRQ>
> > ?warn_alloc.cold.43+0x8a/0x148
> > ?__alloc_pages_nodemask+0x1a5c/0x1bb0
> > ?alloc_pages_current+0x9c/0x110
> > ?allocate_slab+0x34a/0x11f0
> > ?new_slab+0x46/0x70
> > ?___slab_alloc+0x604/0x950
> > ?__slab_alloc+0x12/0x20
> > ?kmem_cache_alloc+0x32a/0x400
> > ?__build_skb+0x23/0x60
> > ?build_skb+0x1a/0xb0
> > ?igb_clean_rx_irq+0xafc/0x1010 [igb]
> > ?igb_poll+0x4bb/0xe30 [igb]
> > ?net_rx_action+0x244/0x7a0
> > ?__do_softirq+0x1a0/0x60a
> > ?irq_exit+0xb5/0xd0
> > ?do_IRQ+0x81/0x170
> > ?common_interrupt+0xf/0xf
> > ?</IRQ>
> > 
> > Since it has no __GFP_NOWARN to begin with, it will call,

I think that DEFAULT_RATELIMIT_INTERVAL and DEFAULT_RATELIMIT_BURST
are good when we ratelimit just a single printk() call, so the ratelimit
is "max 10 kernel log lines in 5 seconds".

But the thing is different in case of dump_stack() + show_mem() +
some other output. Because now we ratelimit not a single printk() line,
but hundreds of them. The ratelimit becomes - 10 * $$$ lines in 5 seconds
(IOW, now we talk about thousands of lines). Significantly more permissive
ratelimiting.

	-ss