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Wed, 04 Sep 2019 00:19:15 -0700 (PDT) Received: from localhost ([175.223.23.37]) by smtp.gmail.com with ESMTPSA id s5sm21619783pfm.97.2019.09.04.00.19.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Sep 2019 00:19:14 -0700 (PDT) Date: Wed, 4 Sep 2019 16:19:11 +0900 From: Sergey Senozhatsky To: Michal Hocko Cc: Sergey Senozhatsky , Qian Cai , Eric Dumazet , davem@davemloft.net, netdev@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Petr Mladek , Sergey Senozhatsky , Steven Rostedt Subject: Re: [PATCH] net/skbuff: silence warnings under memory pressure Message-ID: <20190904071911.GB11968@jagdpanzerIV> References: <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> <20190904064144.GA5487@jagdpanzerIV> <20190904065455.GE3838@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190904065455.GE3838@dhcp22.suse.cz> User-Agent: Mutt/1.12.1 (2019-06-15) X-Bogosity: Ham, tests=bogofilter, spamicity=0.003763, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On (09/04/19 08:54), Michal Hocko wrote: > I am sorry, I could have been more explicit when CCing you. Oh, sorry! My bad! > Sure the ratelimit is part of the problem. But I was more interested > in the potential livelock (infinite loop) mentioned by Qian Cai. It > is not important whether we generate one or more lines of output from > the softirq context as long as the printk generates more irq processing > which might end up doing the same. Is this really possible? Hmm. I need to look at this more... wake_up_klogd() queues work only once on particular CPU: irq_work_queue(this_cpu_ptr(&wake_up_klogd_work)); bool irq_work_queue() { /* Only queue if not already pending */ if (!irq_work_claim(work)) return false; __irq_work_queue_local(work); } softirqs are processed in batches, right? The softirq batch can add XXXX lines to printk logbuf, but there will be only one PRINTK_PENDING_WAKEUP queued. Qian Cai mentioned that "net_rx_action softirqs again which are plenty due to connected via ssh etc." so the proportion still seems to be N:1 - we process N softirqs, add 1 printk irq_work. But need to think more. Interesting question. -ss