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[209.85.220.65]) by mx.google.com with SMTPS id p23sor3502704qtn.56.2019.03.15.11.49.05 for (Google Transport Security); Fri, 15 Mar 2019 11:49:05 -0700 (PDT) Received-SPF: pass (google.com: domain of joel@joelfernandes.org designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@joelfernandes.org header.s=google header.b=XlCmr86N; spf=pass (google.com: domain of joel@joelfernandes.org designates 209.85.220.65 as permitted sender) smtp.mailfrom=joel@joelfernandes.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=jDVu9oumcNkqVWq1A9ByqO3eErH+1lF+kli+4UwjDSo=; b=XlCmr86Nfgg3xBxju2EZKTlTIuahwPKKbKnb6AAlhmp/tbiXOHmzB9Z4TTY65xaPhY h4du8n5E8MqaLaMPiBzkN0MAjbdzjR75E/AcT2yQNsgUl/sytZ2UHw3nW5f5SaJzdt7G qzWXFPPAMKCh8WrfHRT1c/0etmimiPLKZ6KAE= X-Google-Smtp-Source: APXvYqw8pCjTHPS+C/nJz1ilQ/4K2gffZ1/50M17YBUUilptOjlnj0xzZ/lMuV0kS8T6iuWCBA4H8g== X-Received: by 2002:ac8:3042:: with SMTP id g2mr4025863qte.1.1552675745275; Fri, 15 Mar 2019 11:49:05 -0700 (PDT) Received: from localhost ([2620:0:1004:1100:cca9:fccc:8667:9bdc]) by smtp.gmail.com with ESMTPSA id m88sm1384596qte.68.2019.03.15.11.49.04 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 15 Mar 2019 11:49:04 -0700 (PDT) Date: Fri, 15 Mar 2019 14:49:03 -0400 From: Joel Fernandes To: Christian Brauner Cc: Daniel Colascione , Steven Rostedt , Sultan Alsawaf , Tim Murray , Michal Hocko , Suren Baghdasaryan , Greg Kroah-Hartman , Arve =?iso-8859-1?B?SGr4bm5lduVn?= , Todd Kjos , Martijn Coenen , Ingo Molnar , Peter Zijlstra , LKML , "open list:ANDROID DRIVERS" , linux-mm , kernel-team Subject: Re: [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android Message-ID: <20190315184903.GB248160@google.com> References: <20190312080532.GE5721@dhcp22.suse.cz> <20190312163741.GA2762@sultan-box.localdomain> <20190314204911.GA875@sultan-box.localdomain> <20190314231641.5a37932b@oasis.local.home> <20190315180306.sq3z645p3hygrmt2@brauner.io> <20190315181324.GA248160@google.com> <20190315182426.sujcqbzhzw4llmsa@brauner.io> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190315182426.sujcqbzhzw4llmsa@brauner.io> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Mar 15, 2019 at 07:24:28PM +0100, Christian Brauner wrote: [..] > > why do we want to add a new syscall (pidfd_wait) though? Why not just use > > standard poll/epoll interface on the proc fd like Daniel was suggesting. > > AFAIK, once the proc file is opened, the struct pid is essentially pinned > > even though the proc number may be reused. Then the caller can just poll. > > We can add a waitqueue to struct pid, and wake up any waiters on process > > death (A quick look shows task_struct can be mapped to its struct pid) and > > also possibly optimize it using Steve's TIF flag idea. No new syscall is > > needed then, let me know if I missed something? > > Huh, I thought that Daniel was against the poll/epoll solution? Hmm, going through earlier threads, I believe so now. Here was Daniel's reasoning about avoiding a notification about process death through proc directory fd: http://lkml.iu.edu/hypermail/linux/kernel/1811.0/00232.html May be a dedicated syscall for this would be cleaner after all. > I have no clear opinion on what is better at the moment since I have > been mostly concerned with getting pidfd_send_signal() into shape and > was reluctant to put more ideas/work into this if it gets shutdown. > Once we have pidfd_send_signal() the wait discussion makes sense. Ok. It looks like that is almost in though (fingers crossed :)). thanks, - Joel