From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael Kerrisk (man-pages)" Subject: Re: cgroups(7): documenting cgroups v2 thread mode Date: Tue, 9 Jan 2018 23:54:03 +0100 Message-ID: <5c9ea5dd-12dc-99d6-7905-40fdbc34e6ae@gmail.com> References: <20180109211000.GT3668920@devbig577.frc2.facebook.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20180109211000.GT3668920@devbig577.frc2.facebook.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Tejun Heo Cc: mtk.manpages@gmail.com, Peter Zijlstra , cgroups@vger.kernel.org, lkml , linux-man , "Serge E. Hallyn" , Mike Galbraith , Li Zefan , Ingo Molnar , Paul Turner , kernel-team@fb.com, Andy Lutomirski , Johannes Weiner , Lauro Venancio , Waiman Long List-Id: linux-man@vger.kernel.org On 01/09/2018 10:10 PM, Tejun Heo wrote: > Hello, > > On Tue, Jan 02, 2018 at 07:24:01PM +0100, Michael Kerrisk (man-pages) wrote: >> 2. We write the string "threaded" to each of the domain invalid >> cgroups under y, in order to convert them to the type >> threaded. As a consequence of this step, all threads under >> the threaded root now have the type threaded and the >> threaded subtree is now fully usable. The requirement to >> write "threaded" to each of these cgroups is somewhat cum‐ >> bersome, but allows for possible future extensions to the >> thread-mode model. >> >> ┌─────────────────────────────────────────────────────┐ >> │FIXME │ >> ├─────────────────────────────────────────────────────┤ >> │Re the preceding paragraphs... Are there other rea‐ │ >> │sosn for the (cumbersome) requirement to write │ >> │'threaded' to each of the cgroup.type files in the │ >> │threaded subtrees? Tejun Heo mentioned the follow‐ │ >> │ing: │ >> │ │ >> │ Consistency w/ the cgroups right under the root │ >> │ cgroup. Because they can be both domains and │ >> │ threadroots, we can't switch the children over │ >> │ to thread mode automatically. Doing that for │ >> │ cgroups further down in the hierarchy would be │ >> │ really inconsistent. │ >> │ │ >> │But, it's not clear to me how "Doing that for │ >> │cgroups further down in the hierarchy would be │ >> │really inconsistent", since in the current implemen‐ │ >> │tation, those same thread groups are converted to │ >> │"domain invalid" type. What am I missing? │ >> └─────────────────────────────────────────────────────┘ > > Yeah, I was confused with an earlier varient where we were marking > threaded domains instead of threaded roots. It's mostly about future > extensibility (especially as Waiman was proposing related changes > there) and not doing things automatically / recursively if possible. > > Looks good to me. One more thing. I added the following sentence to the text: The cgroup.threads file is writable only for the cgroups inside a threaded subtree. Can you confirm that that is correct, please. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/