Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758785Ab0FVBmg (ORCPT ); Mon, 21 Jun 2010 21:42:36 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:52062 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752630Ab0FVBme (ORCPT ); Mon, 21 Jun 2010 21:42:34 -0400 Date: Mon, 21 Jun 2010 18:41:16 -0700 From: Andrew Morton To: Roland McGrath Cc: Edward Allcutt , Alexander Viro , Randy Dunlap , Jiri Kosina , Dave Young , Martin Schwidefsky , "H. Peter Anvin" , Oleg Nesterov , KOSAKI Motohiro , Neil Horman , Ingo Molnar , Peter Zijlstra , "Eric W. Biederman" , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] fs: limit maximum concurrent coredumps Message-Id: <20100621184116.92f85696.akpm@linux-foundation.org> In-Reply-To: <20100622012303.BD72E402AD@magilla.sf.frob.com> References: <1277164737-30055-1-git-send-email-edward@allcutt.me.uk> <20100622012303.BD72E402AD@magilla.sf.frob.com> X-Mailer: Sylpheed 2.7.1 (GTK+ 2.18.9; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2524 Lines: 53 On Mon, 21 Jun 2010 18:23:03 -0700 (PDT) Roland McGrath wrote: > A core dump is just an instance of a process suddenly reading lots of its > address space and doing lots of filesystem writes, producing the kinds of > thrashing that any such instance might entail. It really seems like the > real solution to this kind of problem will be in some more general kind of > throttling of processes (or whatever manner of collections thereof) when > they got hog-wild on page-ins or filesystem writes, or whatever else. I'm > not trying to get into the details of what that would be. But I have to > cite this hack as the off-topic kludge that it really is. That said, I do > certainly sympathize with the desire for a quick hack that addresses the > scenario you experience. yup. > For the case you described, it seems to me that constraining concurrency > per se would be better than punting core dumps when too concurrent. That > is, you should not skip the dump when you hit the limit. Rather, you > should block in do_coredump() until the next dump already in progress > finishes. (It should be possible to use TASK_KILLABLE so that those dumps > in waiting can be aborted with a follow-on SIGKILL. But Oleg will have to > check on the signals details being right for that.) yup. Might be able to use semaphores for this. Use sema_init(), down_killable() and up(). Modifying the max concurrency value would require a loop of up()s and down()s, probably all surrounded by a mutex_lock. Which is a bit ugly, and should be done in kernel/semaphore.c I guess. > That won't make your crashers each complete quickly, but it will prevent > the thrashing. Instead of some crashers suddenly not producing dumps at > all, they'll just all queue up waiting to finish crashing but not using any > CPU or IO resources. That way you don't lose any core dumps unless you > want to start SIGKILL'ing things (which oom_kill might do if need be), > you just don't die in flames trying to do nothing but dump cores. A global knob is a bit old-school. Perhaps it should be a per-memcg knob or something. otoh, one could perhaps toss all these tasks into a blkio_cgroup and solve this problem with the block IO controller. After all, that's what it's for. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/