From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Gushchin Subject: Re: cgroups(7): documenting cgroup.stat Date: Tue, 2 Jan 2018 21:57:33 +0000 Message-ID: <20180102215726.GA2606@castle> References: <196c0cca-b573-8c65-2b5f-66376f79a836@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : content-transfer-encoding : in-reply-to; s=facebook; bh=3+1X9mnndx9+oVhCHiSfbaebIiYoIXK6vcz/xamKB8w=; b=cvB89ilIep8KRHFt/dZrMbcEVjpZyGQg45vUs4uqnmd2xrgyvGpP6C66xb+X61zW2jqE 8cQyC9lJl5QM5uabV1dAmiBXcmpRQGYNBhGa9AZlwm5NMCs74UIr38GQucEslrl1P5G/ Iw/Q7V91B46BtH6OJonlSViyWMtoqr3exE0= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.onmicrosoft.com; s=selector1-fb-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version; bh=3+1X9mnndx9+oVhCHiSfbaebIiYoIXK6vcz/xamKB8w=; b=a4rq8ykeRF3lsjWAX3xT7mj8AxbocLB1uXaqu6WC73pqCSi2uw3FzV4ZOSiJX+iRTmQpE6q7HyYj6RF8Lm5Df/HVSlHYqBJU3k/+MaPO79dpZe9FQqp1F30GeU/3jqaOGUX9TVIC0xBWLy1z4UKDywoPAencPo6x/apUSi9/gzs= Content-Disposition: inline In-Reply-To: <196c0cca-b573-8c65-2b5f-66376f79a836-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: linux-man-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: To: "Michael Kerrisk (man-pages)" Cc: Tejun Heo , "Serge E. Hallyn" , lkml , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-man Hello, Michael! Thank you for working on this! Please, find my comments below. On Tue, Jan 02, 2018 at 07:22:33PM +0100, Michael Kerrisk (man-pages) wrote: > Hello Roman, > > I wish to add documentation to cgroups(7) for the cgroup.stat file > that you added in Linux 4.14. I wrote some text based on your text > added to the cgroup-v2.txt file, but added some pieces, and also have > a question (see below). The plain-text version for (easy review) > is shown below. Could you please review this text? (Please note > the FIXME!) > > The branch containing the pending cgroups(7) changes can be found at : > https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/log/?h=draft_cgroup_updates > > [[ > Cgroups v2 cgroup.stat file > Each cgroup in the v2 hierarchy contains a read-only > cgroup.stat file (first introduced in Linux 4.14) that consists > of lines containing key-value pairs. The following keys cur‐ > rently appear in this file: > > nr_descendants > This is the total number of visible (i.e., living) > descendant cgroups underneath this cgroup. > > ┌─────────────────────────────────────────────────────┐ > │FIXME │ > ├─────────────────────────────────────────────────────┤ > │For the following text on nr_dying_descendants, it │ > │would I think be helpful to describe a condrete │ > │example of when one might see nr_dying_descendants a │ > │nonzero value for this key. Ideally, the example │ > │would be one that the reader could easily reproduce. │ > │Is there such an example? │ > └─────────────────────────────────────────────────────┘ Hm, basically any cgroup which had some pagecache, associated during the lifetime, will spend some time in the dying state. This means that for most cgroups this number will be non-zero for some amount of time, which depends on global memory pressure. It's also very implementation-defined, and will be likely changed in the following kernel versions. So, I'm not sure, that such an example will be useful for a user. Until this number is huge and constantly growing, it shouldn't be interesting for an user at all. > > nr_dying_descendants > This is the total number of dying descendant cgroups > underneath this cgroup. A cgroup enters the dying state > after being deleted. It remains in that state for an > undefined period (which will depend on system load) > before being destroyed. > > A process can't be made a member of a dying cgroup, and > a dying cgroup can't be brought back to life. So, maybe it worth it to add a statement, that some amount of dying cgroups is normal and it's not a signal of any problem? Otherwise looks very good to me. Thank you! Roman -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html