From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id D86C28D0017 for ; Sun, 14 Nov 2010 16:29:57 -0500 (EST) Received: from hpaq7.eem.corp.google.com (hpaq7.eem.corp.google.com [172.25.149.7]) by smtp-out.google.com with ESMTP id oAELTtRg001234 for ; Sun, 14 Nov 2010 13:29:56 -0800 Received: from pxi4 (pxi4.prod.google.com [10.243.27.4]) by hpaq7.eem.corp.google.com with ESMTP id oAELTmfe019635 for ; Sun, 14 Nov 2010 13:29:54 -0800 Received: by pxi4 with SMTP id 4so1220584pxi.2 for ; Sun, 14 Nov 2010 13:29:48 -0800 (PST) Date: Sun, 14 Nov 2010 13:29:44 -0800 (PST) From: David Rientjes Subject: Re: [PATCH v2]mm/oom-kill: direct hardware access processes should get bonus In-Reply-To: <20101112104140.DFFF.A69D9226@jp.fujitsu.com> Message-ID: References: <1289305468.10699.2.camel@localhost.localdomain> <20101112104140.DFFF.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: "Figo.zhang" , lkml , "linux-mm@kvack.org" , Andrew Morton , Linus Torvalds List-ID: On Sun, 14 Nov 2010, KOSAKI Motohiro wrote: > > So the question that needs to be answered is: why do these threads deserve > > to use 3% more memory (not >4%) than others without getting killed? If > > there was some evidence that these threads have a certain quantity of > > memory they require as a fundamental attribute of CAP_SYS_RAWIO, then I > > have no objection, but that's going to be expressed in a memory quantity > > not a percentage as you have here. > > 3% is choosed by you :-/ > No, 3% was chosen in __vm_enough_memory() for LSMs as the comment in the oom killer shows: /* * Root processes get 3% bonus, just like the __vm_enough_memory() * implementation used by LSMs. */ and is described in Documentation/filesystems/proc.txt. I think in cases of heuristics like this where we obviously want to give some bonus to CAP_SYS_ADMIN that there is consistency with other bonuses given elsewhere in the kernel. > Old background is very simple and cleaner. > The old heuristic divided the arbitrary badness score by 4 with CAP_SYS_RESOURCE. The new heuristic doesn't consider it. How is that more clean? > CAP_SYS_RESOURCE mean the process has a privilege of using more resource. > then, oom-killer gave it additonal bonus. > As a side-effect of being given more resources to allocate, those applications are relatively unbounded in terms of memory consumption to other tasks. Thus, it's possible that these applications are using a massive amount of memory (say, 75%) and now with the proposed change a task using 25% of memory would be killed instead. This increases the liklihood that the CAP_SYS_RESOURCE thread will have to be killed eventually, anyway, and the goal is to kill as few tasks as possible to free sufficient amount of memory. Since threads having CAP_SYS_RESOURCE have full control over their oom_score_adj, they can take the additional precautions to protect themselves if necessary. It doesn't need to be a part of the heuristic to bias these tasks which will lead to the undesired result described above by default rather than intentionally from userspace. > CAP_SYS_RAWIO mean the process has a direct hardware access privilege > (eg X.org, RDB). and then, killing it might makes system crash. > Then you would want to explicitly filter these tasks from oom kill just as OOM_SCORE_ADJ_MIN works rather than giving them a memory quantity bonus. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org