From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CE805C433FF for ; Mon, 29 Jul 2019 15:37:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AAFE02067D for ; Mon, 29 Jul 2019 15:37:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728589AbfG2Pht (ORCPT ); Mon, 29 Jul 2019 11:37:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60733 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725209AbfG2Pht (ORCPT ); Mon, 29 Jul 2019 11:37:49 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DE805300CA4D; Mon, 29 Jul 2019 15:37:48 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-160.bos.redhat.com [10.18.17.160]) by smtp.corp.redhat.com (Postfix) with ESMTP id 11B105C1A1; Mon, 29 Jul 2019 15:37:47 +0000 (UTC) Subject: Re: [PATCH v2] sched/core: Don't use dying mm as active_mm of kthreads To: Peter Zijlstra Cc: Ingo Molnar , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Phil Auld , Rik van Riel , Andy Lutomirski References: <20190727171047.31610-1-longman@redhat.com> <20190729085235.GT31381@hirez.programming.kicks-ass.net> <4cd17c3a-428c-37a0-b3a2-04e6195a61d5@redhat.com> <20190729150338.GF31398@hirez.programming.kicks-ass.net> From: Waiman Long Organization: Red Hat Message-ID: Date: Mon, 29 Jul 2019 11:37:47 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190729150338.GF31398@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Mon, 29 Jul 2019 15:37:48 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/29/19 11:03 AM, Peter Zijlstra wrote: > On Mon, Jul 29, 2019 at 10:51:51AM -0400, Waiman Long wrote: >> On 7/29/19 4:52 AM, Peter Zijlstra wrote: >>> On Sat, Jul 27, 2019 at 01:10:47PM -0400, Waiman Long wrote: >>>> It was found that a dying mm_struct where the owning task has exited >>>> can stay on as active_mm of kernel threads as long as no other user >>>> tasks run on those CPUs that use it as active_mm. This prolongs the >>>> life time of dying mm holding up memory and other resources like swap >>>> space that cannot be freed. >>> Sure, but this has been so 'forever', why is it a problem now? >> I ran into this probem when running a test program that keeps on >> allocating and touch memory and it eventually fails as the swap space is >> full. After the failure, I could not rerun the test program again >> because the swap space remained full. I finally track it down to the >> fact that the mm stayed on as active_mm of kernel threads. I have to >> make sure that all the idle cpus get a user task to run to bump the >> dying mm off the active_mm of those cpus, but this is just a workaround, >> not a solution to this problem. > The 'sad' part is that x86 already switches to init_mm on idle and we > only keep the active_mm around for 'stupid'. > > Rik and Andy were working on getting that 'fixed' a while ago, not sure > where that went. Good, perhaps the right thing to do is for the idle->kernel case to keep init_mm as the active_mm instead of reuse whatever left behind the last time around. Cheers, Longman